about:memory AdBlock Plus Firefox Memory consumption MemShrink

Firefox 41 will use less memory when running AdBlock Plus

Last year I wrote about AdBlock Plus’s effect on Firefox’s memory usage. The most important part was the following.

First, there’s a constant overhead just from enabling ABP of something like 60–70 MiB. […] This appears to be mostly due to additional JavaScript memory usage, though there’s also some due to extra layout memory.

Second, there’s an overhead of about 4 MiB per iframe, which is mostly due to ABP injecting a giant stylesheet into every iframe. Many pages have multiple iframes, so this can add up quickly. For example, if I load TechCrunch and roll over the social buttons on every story […], without ABP, Firefox uses about 194 MiB of physical memory. With ABP, that number more than doubles, to 417 MiB.

An even more extreme example is this page, which contains over 400 iframes. Without ABP, Firefox uses about 370 MiB. With ABP, that number jumps to 1960 MiB.

(This description was imprecise; the overhead is actually per document, which includes both top-level documents in a tab and documents in iframes.)

Last week Mozilla developer Cameron McCormack landed patches to fix bug 77999, which was filed more than 14 years ago. These patches enable sharing of CSS-related data — more specifically, they add data structures that share the results of cascading user agent style sheets — and in doing so they entirely fix the second issue, which is the more important of the two.

For example, on the above-mentioned “extreme example” (a.k.a. the Vim Color Scheme Test) memory usage dropped by 3.62 MiB per document. There are 429 documents on that page, which is a total reduction of about 1,550 MiB, reducing memory usage for that page down to about 450 MiB, which is not that much more than when AdBlock Plus is absent. (All these measurements are on a 64-bit build.)

I also did measurements on various other sites and confirmed the consistent saving of ~3.6 MiB per document when AdBlock Plus is enabled. The number of documents varies widely from page to page, so the exact effect depends greatly on workload. (I wanted to test TechCrunch again, but its front page has been significantly changed so it no longer triggers such high memory usage.) For example, for one of my measurements I tried opening the front page and four articles from each of, and, for a total of 15 tabs. With Cameron’s patches applied Firefox with AdBlock Plus used about 90 MiB less physical memory, which is a reduction of over 10%.

Even when AdBlock Plus is not enabled this change has a moderate benefit. For example, in the Vim Color Scheme Test the memory usage for each document dropped by 0.09 MiB, reducing memory usage by about 40 MiB.

If you want to test this change out yourself, you’ll need a Nightly build of Firefox and a development build of AdBlock Plus. (Older versions of AdBlock Plus don’t work with Nightly due to a recent regression related to JavaScript parsing). In Firefox’s about:memory page you’ll see the reduction in the “style-sets” measurements. You’ll also see a new entry under “layout/rule-processor-cache”, which is the measurement of the newly shared data; it’s usually just a few MiB.

This improvement is on track to make it into Firefox 41, which is scheduled for release on September 22, 2015. For users on other release channels, Firefox 41 Beta is scheduled for release on August 11, and Firefox 41 Developer Edition is scheduled to be released in the next day or two.

AdBlock Plus Firefox Memory consumption

AdBlock Plus’s effect on Firefox’s memory usage

[Update: Wladimir Palant has posted a response on the AdBlock Plus blog. Also, a Chrome developer using the handle “Klathmon” has posted numerous good comments in the Reddit discussion of this post, explaining why ad-blockers are inherently CPU- and memory-intensive, and why integrating ad-blocking into a browser wouldn’t necessarily help.]

AdBlock Plus (ABP) is the most popular add-on for Firefox. AMO says that it has almost 19 million users, which is almost triple the number of the second most popular add-on. I have happily used it myself for years — whenever I use a browser that doesn’t have an ad blocker installed I’m always horrified by the number of ads there are on the web.

But we recently learned that ABP can greatly increase the amount of memory used by Firefox.

First, there’s a constant overhead just from enabling ABP of something like 60–70 MiB. (This is on 64-bit builds; on 32-bit builds the number is probably a bit smaller.) This appears to be mostly due to additional JavaScript memory usage, though there’s also some due to extra layout memory.

Second, there’s an overhead of about 4 MiB per iframe, which is mostly due to ABP injecting a giant stylesheet into every iframe. Many pages have multiple iframes, so this can add up quickly. For example, if I load TechCrunch and roll over the social buttons on every story (thus triggering the loading of lots of extra JS code), without ABP, Firefox uses about 194 MiB of physical memory. With ABP, that number more than doubles, to 417 MiB. This is despite the fact that ABP prevents some page elements (ads!) from being loaded.

An even more extreme example is this page, which contains over 400 iframes. Without ABP, Firefox uses about 370 MiB. With ABP, that number jumps to 1960 MiB. Unsurprisingly, the page also loads more slowly with ABP enabled.

So, it’s clear that ABP greatly increases Firefox’s memory usage. Now, this isn’t all bad. Many people (including me!) will be happy with this trade-off — they will gladly use extra memory in order to block ads. But if you’re using a low-end machine without much memory, you might have different priorities.

I hope that the ABP authors can work with us to reduce this overhead, though I’m not aware of any clear ideas on how to do so. In the meantime, it’s worth keeping these measurements in mind. In particular, if you hear people complaining about Firefox’s memory usage, one of the first questions to ask is whether they have ABP installed.

[A note about the comments: I have deleted 17 argumentative, repetitive, borderline-spam comments from a single commenter — after giving him a warning via email — and I will delete any further comments from him on this post. As a result, I also had to delete three replies to his comments from others, for which I apologize.]

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MemShrink progress, week 49-50

System Compartment Reporting

With the recent landing of compartment-per-global, Firefox now regularly has 200+ system compartments at start-up.  However, most of these compartments didn’t have names, which meant that they were merged into a single “[System Principal]” entry in about:memory and about:compartments.

Until last week, that is, when Nils Maier added identifying information to the vast majority of these.  Here’s a small selection of interesting ones from about:compartments on my own machine.














Just from this, it’s obvious that I had about:compartments and about:memory?verbose open at the time.  It’s also obvious that I had the following add-ons installed:  AdBlock Plus, Chatzilla, Tree Style Tab, and pdf.js.  And about:memory now gives at least a partial measurement of how much memory these add-ons are using.  This will help identify add-ons that are using excessive amounts of memory.  (Having said that, I identified the add-on compartments simply by their names.  It’d be great if there was a way to systematically identify them within the code, but I don’t know if that’s possible.)

I also hope people will scrutinize Firefox’s own compartment use closely, and start to file bug reports saying things like “hey, that .jsm module shouldn’t be present, there must be a leak”.  If you want to see what the full list of 200+ looks like, try out a recent Nightly build!

In related news, I also added some new compartment-specific reports, including ones for cross-compartment wrappers.

One consequence of all these change is that the number of entries in about:memory jumped tremendously.  As a result, I aggregated the small entries within each compartment, which reduces the number of entries by a factor of roughly four while still reporting full information for large compartments.  Nils and I also made about:memory more efficient, so the amount of memory required to generate each line dropped by about 20%.  about:memory still takes up memory itself, but it does so at a level that I’m fairly happy with.


For a change, the biggest MemShrink-related news in this report wasn’t related to add-ons!  But there was still some interesting movement there.

Justin Lebar uncovered some evidence that the Hueyfix is having a real, positive effect among users.  Telemetry data from Nightly users shows that the number of ghost windows — a concept for which we don’t have good documentation, but they correlate with zombie compartments — has dropped dramatically, as the following graph shows.

ghost windows telemetry data graph

Telemetry data tends to be extremely noisy, so it’s nice to see a clear signal — Kyle’s change made it into Nightly builds on May 5th [Update: that’s incorrect, see below] and immediately caused the mean number of ghost windows to drop from roughly three to roughly one.  The variance also dropped dramatically.

Update: Justin just wrote a blog post that explains very nicely what ghost windows are.  That post also explains better the circumstances behind the drop in ghost window numbers;  my explanation above was too simple and got the timing wrong.  Thanks, Justin!

In other add-on news, the following add-ons had leaks fixed: Readability, ProxTube, Youtube MP3 Podcaster.

Firefox vs The New York Times

Robert O’Callahan fixed a leak relating to mouse events that triggered when he visited  He wrote a great blog post explaining the heroic debugging — searching through full memory dumps! — that was required.  It’s great that Robert found and fixed this, though it’s a shame it took such expertise.

Bug Counts

Here are the current bug counts.

  • P1: 23 (-1/+2)
  • P2: 85 (-2/+4)
  • P3: 102 (-5/+2)
  • Unprioritized: 2 (-3/+2)

Not a great deal of movement.  We only had to triage twelve bugs in today’s MemShrink meeting, which is the fewest we’ve had since we switched to fortnightly meetings.

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MemShrink progress, week 32

There wasn’t much MemShrink activity this week in terms of bugs fixed, just bug 718100 and bug 720359.  So I’m going to take the opportunity this week to talk about the bigger picture.

Bug Counts

As a prelude, here are this week’s bug counts.

  • P1: 20 (-4/+0)
  • P2: 131 (-3/+3)
  • P3: 74 (-2/+7)
  • Unprioritized: 4 (-3/+4)

The drop in P1s was just due to bug re-classification;  in particular, three bugs relating to long cycle collector pauses were un-MemShrink’d because they are more about responsiveness, and they are being tracked by Project Snappy.

The Big Ticket Items

David Mandelin asked me today what where the big ticket items for MemShrink.  I’d been looking a lot at the MemShrink:P1 list recently (which is why some were re-classified) and so I was able to break it down into six main areas that cover most of the P1s and various P2s.  I’ll list these from what I think is least important to most important.

#6: Better Script Handling

Internally, a JSScript represents (more or less) the code of a JS function, including things like the internal bytecode that SpiderMonkey generates for it.  The memory used by JSScripts is measured by the “gc-heap/scripts” and “script-data” entries in about:memory.

Luke Wagner did some measurements that showed that most (70–80%) JSScripts created in the browser are never run.  In hindsight, this isn’t so surprising — many websites load libraries like jQuery but only use a fraction of the functions in those libraries.  If SpiderMonkey could be changed to generate bytecode for scripts lazily, it could reduce “script-data” memory usage by 60–70%.  This would also allow the decompiler to be removed, which would be great.

Luke also proposed sharing immutable parts of scripts between web pages.  This would avoid a lot of duplication in the case where you have many tabs open with pages from a single site.

Both of these changes potentially will make the browser faster as well, because SpiderMonkey will spend less time compiling JavaScript source code to bytecode.

No-one is assigned to work on these bugs.  The lazy script creation can be done entirely within the JS engine;  the script sharing requires assistance from Necko.  Luke is currently busy with some other righteous refactorings, but I’m quietly hoping once they’re done he might find time for one or both of these bugs.

#5: Better Memory Reporting

Before you can reduce memory consumption you have to measure it.  about:memory is the critical tool that has facilitated much of MemShrink’s work.  (For example, we never would have known about zombie compartments without it.)  It’s in pretty good shape now but there are two major improvements that can be made.

First, the “heap-unclassified” number (a.k.a “dark matter”) is still typically around 20–25%.  My goal is to reduce that to 10%. This won’t require any great new insights, we already have the tools and data required.  Rather, it’s just a matter of grinding through the list of memory reporters that need to be added and improved.

Second, the resources used by each browser tab are reported in an unwieldy fashion:  JS memory on a per-compartment basis;  layout memory on a per-docshell basis;  DOM memory on a per-window basis.  Only a few internal architectural changes stand in the way of uniting these to provide the oft-requested feature of per-tab memory reporting.  This will be great for users, because if Firefox is using more memory than they’d like, it tells them which tabs they should close in order to free up memory.

I am actively working on both these improvements, and I’m hoping that within a couple of months they’ll be mostly done.

#4: Better Memory Consumption Tracking

One thing we haven’t done well in MemShrink is to improve the state of tracking Firefox’s memory consumption.  We have plenty of anecdotes but not much hard data about the improvements we’ve made, and we don’t have good ways to detect any regressions.  A couple of ideas haven’t gone very far, but some good news is that John Schoenick is making great progress on a proper implementation.  John has demonstrated preliminary versions of the site at two MemShrink meetings and it’s looking very promising.  It uses the endurance test framework to make the measurements, and opens lots of pages from the Talos tp5 pageset.

We also hope to use telemetry data to analyze how the memory consumption of each released version of Firefox stacks up.  That analysis would come with a significant delay — weeks or months after each release — but it would be much more comprehensive than any oft-run benchmark, coming from the real-world usage patterns of thousands of users.

#3: Compacting Generational GC

If you look in about:memory, JavaScript memory usage usually dominates.  In particular, the “js-gc-heap” is usually large.  There’s also the “js-gc-heap-unused-fraction” number, often 30% or higher, which tells you how much of that space is unused because of fragmentation.  That percentage overstates things somewhat, because often a good proportion of that unused space (see “js-gc-heap-decommitted”) is decommitted, which means that it’s costing nothing but address space… but that is cold comfort if you’re suffering out-of-memory aborts on Windows due to virtual memory exhaustion.

A compacting garbage collector is one that can move objects around the heap, filling up all those little gaps that constitute fragmentation.  The JS team (especially Bill McCloskey and Terrence Cole) is implementing a compacting generational garbage collector, which is a particular kind that tends to have good performance.  In particular, many objects die young and generational collectors find these quickly, which means that the heap will grow at a significantly slower rate than it currently does.  I could be wrong, but I’m convinced this will be a big win for both memory consumption and speed.

#2: Better Foreground Tab Image Handling

Images are stored in a compressed format (e.g. JPEG, PNG, GIF) on disk.  In order to display them, a browser must decompress (a.k.a decode) the compressed form into a raw pixel form that can easily be ten times larger.  This decoded form can be discarded and regenerated as necessary, and there are trade-offs to be made — for example, if you are too aggressive in discarding decoded images, you might have to decode them again, which will take CPU cycles and the user might see flickering if the decoding occurs in the visible part of the page.

However, Firefox goes way too far in the other direction.  If you open a page in the foreground tab, every single image in that page will be immediately decoded, and none of the decoded data will be discarded unless you switch away to another tab.  For pages that contain many images, this is a recipe for horrific memory consumption, and Firefox does much worse than all the other browsers.  So this is a problem that doesn’t rear its head for all users, but it’s terrible for those that are affected.

There are three MemShrink:P1 bugs relating to this:  one about not decoding all images immediately, one about discarding non-visible decoded images after some time, and one about some infrastructure work that is required for the first two.  As far as I know, no progress has been made on these three bugs, and although two of them are assigned they are not being actively worked on.

(See this discussion on the dev-platform mailing list for more details about this topic.)

#1: Better Detection and Notification of Leaky Add-ons

It’s been the case for several months that when a user complains about Firefox consuming an excessive amount of memory, it’s usually because of one or more add-ons, and the “can you try that again in safe mode?” / “oh yeah, that fixes it” dance is getting tiresome.

Many add-ons leak.  Even popular, well-written ones:  in the past few months leaks have been found in Adblock Plus, Video DownloadHelper, GreaseMonkey and Firebug.  That’s four of the top five add-ons on AMO!  We’re now getting several reports about leaky add-ons a week;  in this week’s MemShrink meeting there were four:  TorButton, NoSquint, Customize Your Web, and 1Password.  I strongly suspect the leaks we know about are just the tip of the iceberg.

Although leaks in add-ons are not Mozilla’s fault, they are Mozilla’s problem:  Firefox gets blamed for the sins of its add-ons.  And it’s not just memory consumption;  the story is the same for performance in general.  Here’s the quote of the week, from a user of 1Password:

I only use a handful of extensions and honestly never suspected 1P, however after disabling it I noticed my FireFox performance increased very noticibly. I’ve been running for 48 hours now without the 1P extension in Firefox and wow what a difference. Browsing is faster, switching is faster, memory usage is way down.

I’ve lost count of the number of stories like this that I’ve heard.  How many users have we lost to Chrome because of these issues, I wonder?

(And it’s not just leaks.  See this analysis of 16 add-ons and their effect on memory consumption when Firefox starts.)

One small step towards improving this situation was made this week:  Jorge Villalobos and Andrew Williamson added a “check for memory leaks” item to the AMO review checklist (under “Memory leaks from content”).  And Kris Maglione added some support for this checking in his Extension Test add-on.  This means that add-ons with obvious memory leaks (and many of them are obvious if you are actively looking for them) will not be accepted by AMO.

So that will prevents leaks in some new add-ons and new versions of established add-ons.  What about existing add-ons?  One idea is that AMO could also have a flag that indicates add-ons that have known memory problems (and other performance problems).  (This flag wouldn’t be an automatic thing, it would only be set once a leak has been confirmed, and after giving the author notification and some time to fix the problem.)  So that would also improve things a bit.

But lots of add-ons aren’t hosted on AMO.  Another idea is to have a stronger mechanism, one that informs the user if they have any add-ons installed that are known to cause high memory consumption (or other bad performance problems).  There is an existing mechanism for blocking add-ons that are known to be malware or exceptionally crashy, so hopefully the warnings could piggy-back on top of that.

Then, we need a better way to detect leaky add-ons.  Currently this is entirely done manually — and a couple of excellent contributors have found leaks on multiple add-ons — but I’m hoping that it’ll be possible to do a much more thorough job by analyzing telemetry data to find out which add-ons are correlated with high memory consumption.  That information could be used to trigger manual checking.

Finally, once you know an add-on leaks, it’s not always easy to work out why.  Tools could help a lot here, if they can be made to work well.


I listed six big areas for improvement. If we fixed all of these I think we’d be in a fantastic position.

Three of them (#5 better memory reporting, #4 better memory consumption tracking, #3 compacting generational GC) have people working on them and are in a good state.

Three of them (#6 better script handling, #2 better foreground image tab handling, #1 better detection and notification of leaky add-ons) don’t have people working on them, as far as I know.  If you are willing and have the skills to contribute to any of these areas, please contact me!

And if you think I’ve overestimated or underestimated the importance of any issue, I’d love to hear about it.  Thanks!

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Notes on Reducing Firefox’s Memory Consumption

I gave a talk yesterday at the Browser MiniConf, held in Ballarat, Australia.  Its title was “Notes On Reducing Firefox’s Memory Consumption”.

Below are the slides and notes in a SlideShare embedding. If you find that embedding problematic (some people do) you may prefer to download the PDF version directly.

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MemShrink progress, week 30


This was the week of add-ons in MemShrink-land.

Jared Wein fixed a problem in Firefox that was causing zombie compartments if you viewed a native video with any add-on installed that implements the nsIContentPolicy interface.  Examples of such add-ons are Adblock Plus, GreaseMonkey, and NoScript, which are respectively the #1, #3 and #9 most popular add-ons on AMO!  Welcome to the MemShrink club, Jared.

Speaking of GreaseMonkey, Arantius fixed a bug in it that was causing zombie compartments on some GM scripts when opening a background tabs.

I can’t tell who was responsible for the next fix, because the Add-on SDK folks use Github in a way I don’t understand.   But Myk Melez and/or Gabor Krizsanits greatly reduced the number of compartments used in JetPack-style add-ons.  In one example, the number of compartments dropped from 156 to 8, saving about 20MB of memory.  This was a MemShrink:P1 bug.

Also, as far as I can tell, the same patch also fixed bug 680821 which means that all compartments that hold sandboxes created by JetPack-style add-ons will be marked as belonging to that add-on in about:memory.

Jordan Miner reported that the Delicious Bookmarks add-on is leaking excessive numbers of connections to the Places database.  I tried to reproduce the problem and failed, but I don’t have a Delicious account.  If anyone else who does have a Delicious account is able to reproduce, please let me know or comment in the bug.

Finally, Jorge Villalobos and Andrew Williamson from the add-ons team came to this week’s MemShrink meeting.  We had a very fruitful discussion about how to help add-on authors detect and avoid memory leaks, and how to help add-on users understand which add-ons have high memory consumption.  Stay tuned for more details in the coming weeks!

Three Cheers for New Contributors

Krzysztof Kotlenga, a new contributor, removed an OpenGL cache that was wasting 1GB+ of memory on Linux when hardware acceleration was enabled (it’s currently not enabled by default, but will be at some point in the future).   Great work, Krzysztof!  [Update: I originally wrote WebGL instead of OpenGL, which was incorrect.]

Bug Counts

Here are the current bug counts.

  • P1: 26 (-2/+0)
  • P2: 132 (-14/+3)
  • P3: 67 (-2/+5)
  • Unprioritized: 4 (-0/+4)

That’s a net reduction of six bugs.  The main factor here was that I went through some of our P2s and closed ones that were stale and/or covered by other bugs, and downgraded to P3 a few more that are now known to be less important than we first thought.

Before finishing, I’d like to highlight bug 703427.  Richard Hipp, one of the SQLite developers, has a tiny patch that drastically reduces the amount of memory used by SQLite in Firefox — I ran with it for a while and my SQLite memory consumption dropped from ~15MB to less than 3MB.  The patch also causes a moderate speed drop, but it’s unclear if that speed drop is noticeable to Firefox.  We need someone who understands Firefox’s SQLite usage well to evaluate this patch so that Richard knows if it’s something that should go into a released version of SQLite as an option.  The bug is assigned to Marco Bonardo but he’s currently very busy.  Is there anyway else who knows enough about SQLite to take on this bug?

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MemShrink progress, week 27

Adaptive Memory Behaviour

The biggest news this week was that Justin Lebar landed code to make Firefox’s memory consumption adaptive on Windows.  The code works by wrapping VirtualAlloc() and some similar OS-level allocation functions.  Each time memory is allocated, the amount of available virtual and physical memory is measured by the wrapper.  If either of those amounts are below a threshold, a memory pressure event is triggered, which causes numerous components within Firefox to take steps to reduce their memory consumption.

It might not sound like it, but this is a big deal, and it was a MemShrink:P1 bug.  Firefox runs on a huge variety of machines and devices, and trying to find one-size-fits-all heuristics for discarding regenerable data is a recipe for unhappiness somewhere.  Adaptive behaviour is much better.

The initial settings for this feature are conservative, and some tuning may be needed.

  • The threshold used for virtual memory is 128MB, i.e. if the amount of available virtual memory drops below 128MB a memory pressure event is triggered.  (This number can be changed in about:config via the “memory.low_virtual_memory_threshold_mb” setting.) Hopefully this will reduce the number of OOM crashes that occur on Windows.
  • The threshold used for physical memory is 0, which means that it is currently ignored.  (This number can be changed in about:config via the “memory.low_physical_mem_threshold_mb” setting.) The reason for ignoring it currently is that low physical memory may be caused by a program other than Firefox — we don’t want to start discarding data if Firefox is only using a small fraction of physical memory.  In the future we can probably do better here by triggering memory pressure events if the fraction of physical memory used by Firefox exceeds some threshold;  hopefully this will avoid paging when memory usage is high.
  • Memory pressure events are throttled so they aren’t sent more than once every 10 seconds.  (This number can be changed in about:config via the “memory.low_physical_memory_notification_interval_ms” setting.)  This prevents thrashing in cases where the memory pressure events don’t help reduce memory consumption.

Memory pressure events are also currently unevenly observed — plenty of data could be dropped that currently isn’t — so there is room for improvement there.

Finally, there’s another bug still open to add similar adaptive behaviour on Mac, Linux and Android.  Note also that memory pressure events are also triggered on Android when Firefox goes into the background.


There has been good news for add-ons:  the #1, #6 and #8 most popular add-ons on AMO have all recently seen some MemShrink-related improvements.

Adding memory reporters to add-ons is a really good thing to do, and I plan to write some documentation to encourage other add-on developers to follow suit.  However, if you are an add-on developer and are thinking of doing this, I need to stress one thing:  the reports must have KIND_OTHER so that they end up in the “Other Measurements” list in about:memory.  If they are put in the “explicit” tree, then some memory bytes may be counted twice (once by Firefox, once by the add-on) which will completely screw up about:memory’s results.

Memory Reporters

I landed several improvements to memory reporters.

Bug Counts

Here are the current bug counts.

  • P1: 26 (-2/+1)
  • P2: 139 (-6/+6)
  • P3: 64 (-2/+2)
  • Unprioritized: 0 (-1/+0)

Nice to see the total count drop, even if only by one.

Due to the Christmas break there won’t be a MemShrink meeting nor a MemShrink progress report next week.  I’ll be back in two weeks, enjoy the break!

AdBlock Plus Firefox Google Chrome

Converting a Chrome user to Firefox: a follow-up

I wrote yesterday about how I converted a relative of mine from a Chrome user to a Firefox user.  The post was picked up by the tech press including Tom’s Hardware and Conceivably Tech.  (Tom’s said I “described why getting users back from Chrome may nearly be impossible”, which I think is a laughable exaggeration of what I wrote.)

The good news is that the two major stumbling blocks I faced during the conversion are well on the way to being addressed.

  • The situation with third-party add-ons will be greatly improved in Firefox 8, which is scheduled for release in just a few days (2011-11-08).  The first time it runs, Firefox 8 will present the user with a window that lists all the installed add-ons, distinguishing between add-ons the user installed explicitly and third-party add-ons that they didn’t install explicitly.  The user will be asked to confirm which add-ons they want, and the third-party add-ons will be disabled by default.  The bug for this feature is here, and there is a follow-up bug here.
  • An “import history from Chrome” feature is being worked on right now.  Here is the feature page, a tracking bug, and  two dependent bugs.  The aim was for it to make Firefox 10, which is scheduled for release on 2012-01-31, but it looks like it might not make that release.  Hopefully it will make Firefox 11, which is scheduled for release on 2012-03-13.

Another point raised by commenters was that Chrome has a version of AdBlock Plus.  However, the Chrome version still has major shortcomings compared to the Firefox version.  This page states “We are currently working on providing the same experience for Google Chrome as what you are used to from Firefox. Please keep in mind that we are not there yet and much work still needs to be done. There are also known Google Chrome bugs and limitations that need to be resolved.”  This page lists the major shortcomings.  Maybe those shortcomings will be overcome in the future, but until they are, it’s not a reasonable comparison.

In conclusion, the point of my post yesterday was not to say “OMG Firefox is crap the sky is falling in”, but rather “here’s what happened when I tried this”.  I knew that the two obstacles I listed were being worked on, though I didn’t know the details.  (Many thanks to the commenters who filled me in.)  The fact that they are being worked on and/or have been fixed is rather encouraging.  It’s also worth noting that Firefox’s new rapid release calendar like these make it into the hands of ordinary users only 2 to 3 months after they are implemented.  With the old release calendar, these two improvements wouldn’t have made it into a release until mid-2012 or later.

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Converting a Chrome user to Firefox

[Update: before commenting, you should probably read this follow-up post that clarifies certain things about this post.]

On my recent vacation I was staying with a family member, let’s call her Karen (not her real name).  She was a Google Chrome user, and I managed to convert her to a satisfied Firefox user.  Here’s what I learnt along the way.


Bad things about the experience:

  • The third-party add-ons situation on Windows is awful.
  • We need a “import history from Chrome” feature.

Good things about the experience:

  • Mozilla’s non-profit nature is compelling, if you know about it.
  • AdBlock Plus is great.

The Initial Situation

Karen is a moderately sophisticated computer user. She knows what a browser is, but didn’t know how many there were, who made them, or any notable differences between them.

Her machine that is probably 2 or 3 years old, and runs Windows Vista.  She had used IE in the past (not sure which version) but didn’t like it, switched to Chrome at some point — she didn’t remember how or why — and found it to be much better.  She was running Chrome 14.0.835.202 (no, that’s not an IP address!) which was the latest stable version.

She also had Firefox 3.6.17 installed, but judging from the profile she hadn’t used it much — there was very little history.  She had the following Firefox add-ons installed:

  • Java Console 6.0.20 and 6.0.27.
  • The .NET Framework Assistant.
  • Some media player thing.
  • Some Norton “safe search” toolbar, and Symantec IPS, whatever that is.

(What is the Java Console?  What is the .NET Framework Assistant?  As far as I can tell they are (a) very common and (b) useless.)

I told her that I worked on Firefox and suggested that she try it and she was open to the idea.  I talked about the differences between Firefox and Chrome and some of my work on Firefox.  The thing that caught her attention most was that Mozilla is a non-profit organization.  She hadn’t known this and it appealed to her greatly — she said that browser speed and the non-profit nature were the two most important things to her.  She was also somewhat interested when I said that Firefox had an ad-blocking add-on.  At the end of the conversation, she agreed to let me install Firefox and make it the default browser.

Installing Firefox

I removed the existing Firefox profile manually — I wasn’t sure if this was necessary, but I definitely wanted a fresh profile — and then uninstalled Firefox through the Control Panel.  I then installed Firefox 7.0.1.  (BTW, I stayed with Karen for two weeks at this point, and I had deliberately waited until Firefox 7 was out before doing this because I knew it had much lower memory usage than Firefox 6.)

An unexpected thing was that the Firefox installer asked me to close all the other running programs;  it explained that this would mean that I wouldn’t have to reboot.  I’m used to running Firefox on Mac and Linux so I’m not used to this, but I’m familiar enough with Windows that I wasn’t totally surprised.  Still, it was annoying;  Karen had MS Word and some other programs open and I had to go ask her if I needed to save anything before closing them.  I realize this is Windows’ fault, not Firefox’s, but it was an obstacle.

Starting Firefox

When I started Firefox it asked me if I wanted to make it the default browser and I said yes.  (I explained to Karen how to switch the default browser back to Chrome if she was unhappy with Firefox.)

It also asked me if I wanted to import history/bookmarks/etc from IE.  But there was no equivalent for Chrome!  Karen had a ton of bookmarks in Chrome, but fortunately she said she only used a handful of them so I was able to copy them manually into Firefox’s bookmarks toolbar (which I had to make visible).  I’ve heard that someone is working on an “import from Chrome”  feature to Firefox but I don’t know what the status is.  We need it badly.

Once Firefox started, another unexpected thing was the state of the add-ons in the new profile.  The Symantec add-ons (including the ugly Norton toolbar) were present and enabled.  I had to disable them in about:addons;  I wanted to completely uninstall them but I couldn’t, the “uninstall” button just wasn’t present.  The Java Consoles and the media player were disabled because they were incompatible with 7.0.1, but I was also not able to  uninstall them.  This horrified me.  Is it a Windows-only behaviour?  Whatever the explanation, the default situation in a fresh install was that Firefox had several unnecessary, ugly additions, and it took some effort to remove them.  I’m really hoping that the add-on confirmation screen that has been added to Firefox 8 will help improve this situation, because this was the single worst part of the process.

I then tweaked the location of the home and reload buttons so they were in exactly the same position as in Chrome.  I probably didn’t need to do that, but  with those changes made Firefox’s UI looked very similar to Chrome’s, and I wanted things to be as comfortable for her as possible.

The best part of the process was when I installed AdBlock Plus.  With Karen watching, I visited in Chrome, and I had to skip past a video advertisement before even getting to the front page, and then the front page had heaps of ads.  Then I visited in Firefox — no video, no ads.  It was great!


A week or two later I sent Karen a follow-up email to check that everything was ok.  She said “All is well! The ad blocking is a great feature.”

So, Firefox has a new and happy user, but there were some obstacles along the way, and the outcome probably wouldn’t have been so good if Karen hadn’t had a Firefox expert to help her.