Breakthroughs in the add-on review queues

Jorge Villalobos


The last few months have been dense with big changes in the add-ons world. Just reading this blog and looking at all the new faces and posts should give you a good idea. Today I’d like to show you how these changes have affected the add-on review queues and what you can expect for the future.

These charts show the state of the review queues on a weekly basis, starting on Q4 last year:

Full review queue Preliminary review queue Update queue

The green area represents add-ons that have been waiting under 5 days, yellow between 5 and 10 days, and red over 10 days.

As you can see, we were doing pretty poorly in late 2015. We only had one admin reviewer, Andreas Wagner, whose attention was almost entirely focused on reviewing unlisted add-ons (not included in the charts). We already had a significant backlog of add-ons awaiting admin review, and during this time it got a lot worse. We were looking for new admin reviewers we could get on board as contractors, but most of our attention was focused on extension signing.

Turning the tide

A few things happened that helped us get the review queues under control:

  • We stopped gating unlisted add-on signing by review. This freed Andreas’s time so he could go back to review listed add-ons.
  • Our team (finally!) grew. We now have Philipp Kewisch as our second full time admin reviewer and Noitidart helping part time also as an admin. Other areas of the team also got help, like the AMO dev team and editorial, all of which has afforded us much-needed breathing room and focus.
  • Our volunteer team also ramped up their efforts and kept up with the increased submission rate. During the first few weeks of the year, they averaged over 500 reviews per week! This is an amazing feat, especially to those of us who know about the pains of code review.

The review queues are now almost entirely in the green, which is fantastic (in fact, we’re all green in today’s report). However, it’s reasonable to have some skepticism, since we’ve been here before. We rely on a couple of very active volunteers who do the bulk of the reviews. And we will need to turn more of our attention to unlisted submissions soon (though not to the same extent as before).

Keeping it that way

So, what are we doing to maintain wait times that developers can rely on?

First, we have the staff additions I mentioned earlier. Having a stable admin team contributes greatly because we have a higher baseline even when volunteer activity drops. We also have another part-time opening that we will try to fill soon.

We’ve made some changes to the reviewer tools to encourage more participation from less-active reviewers. The review team has grown significantly in the past couple of months, and we receive new applications all the time. Are you interested in joining us? Please apply!

Finally, I think we’re past the big wave of submissions that happened due to the introduction of extension signing. But we do have a stable and steady increase in developer activity (which is good!).

We’d like to thank the add-on developer community for their immense patience during this time. We know it’s been rough and we’re very grateful that you stuck with us. We’ll keep working hard to make sure this becomes the standard.

March 2016 Featured Add-ons

Scott DeVaney


Pick of the Month: Tab Memory Usage

by Jeremy Schomery
Tab Memory Usage displays the amount of memory used in each of your open tabs.

“Works for me just like the name says, displays memory usage next to the tab name. Simple, awesome.”

Featured: ImTranslator

by Smart Link Corporation
Choose translations in 70+ languages by comparing results from Google, Microsoft, and Babylon translation services. Features also include text-to-speech, dictionary, and back translations.

“I’m on the Web 12 hours a day using Firefox, and I have ImTranslator running all the time.”

Friend of Add-ons: Johann Hofmann

Amy Tsay

Our newest Friend of Add-ons is Johann Hofmann! Johann is active in the Rust ecosystem, and has been contributing to WebExtensions in the past few months. He explains, “I like that the WebExtensions project enables me to have such a big impact on the API that I and many other developers will use in the future.”

Johann has also contributed code to JPM, and is a volunteer AMO reviewer. He enjoys open source projects and explains how he began contributing to add-ons:

“I got into contributing to add-ons when I started to write my own Firefox extensions and noticed small bugs in the tooling, which I managed to fix. I love contributing to open source. I think Mozilla is the perfect place to do open source because it focuses on the people behind the code. Everyone is really welcoming and trying to help you make an impact, in real-life events as much as on IRC.”

Thanks to Johann for making an impact with add-ons.

We encourage you to document your contributions on the Recognition page, which also serves as the nomination vehicle for the Friends of Add-ons features.

How to get a quicker review for add-ons with source code attached

Philipp Kewisch


When submitting an add-on to (AMO), it is sometimes necessary to attach source code in addition to the xpi file. This usually applies to add-ons with obfuscated code, because a reviewer wouldn’t be able to approve an add-on without reviewing what was obfuscated. Since these types of add-ons are more complex to review, I’ve written some tips on what you can do to help them get through the queue faster.

When to attach sources

When the add-on xpi file you upload to (AMO) contains code that is not completely readable by a human, it is probably a good idea to attach sources.

For example, if you used tools like uglifyJS, Google Closure Compiler, browserify or a custom pre-processor, you will have to upload sources. The same goes if you are using js-ctypes or including other binary components.

There are also a few cases where it is actually NOT required and in fact not recommended. If your library only contains third-party minified libraries (like jQuery or Angular), or if the libraries you are calling via js-ctypes are system libraries or open source, please do not upload sources. Instead, provide links to the repositories of the respective libraries.

What happens during reviews

When you attach sources, the add-on is marked for “admin-review”. This means that your sources and are only accessible to a small group of admins. We do this to protect your sources.

A very important aspect of reviewing sources is reproducing the obfuscation. As we need to treat every extension developer the same, we must verify that the source code we reviewed matches the uploaded xpi. If we skip this step, a malware author could provide us with legitimate-looking sources and add a backdoor to the previously minified xpi file.

Here are the steps we take:

  1. Download the sources and extract them.
  2. Run <magic steps>, including minifiers, obfuscators, compilers, or code generators.
  3. Take the output directory from the previous step and compare it with the add-on xpi that has been uploaded.
  4. Review the source code files as we would review any other add-on that does not have sources.

In step 3, we use a diff tool to compare the generated sources to the add-on xpi file. There must be no differences at all. To save time, it is very important to provide us with all the <magic steps>. If you don’t add this, we will have to get in touch with you, and that adds time to the review process.

Providing instructions

The easiest way for you to provide the magic steps is to include a README file in the uploaded sources. If it is just one or two files that are obfuscated, the instructions can be something like “run uglifyjs data/mycoolstuff.js”. If the extension is any more complex, please provide a script that we can run that takes care of everything at once. Things you should mention in your README include:

  • Prerequisites that need to be downloaded separately, for example yuicompressor.
  • For less popular or custom-written build tools, provide links where they can be downloaded, as well as installation steps.
  • If a specific version of supplemental software needs to be used, please let us know. But avoid doing so if the latest version would work just as well.
  • All commands we should run to go from sources to a generated xpi file that matches the one you’ve uploaded, for example npm install or a grunt target.

Please assume the reviewer has a vanilla operating system set up. You don’t need to describe how to install common tools including npm, node, the add-on SDK, but please make sure the reviewer can figure out how to install everything needed to generate the xpi file.

Aside from the README file, you also need to package everything required to build. If your add-on depends on a private repository or frameworks not commonly available, please include them as well.

Desired outcome

Common build tools used are make, grunt, gulp and ant. If you don’t already have a build target that runs the above steps, please add a target that does so. For example, allow us to run grunt firefox-dist to create the generated xpi. Here is an example of what the sources could look like. The dist directory is initially empty, until your build script (in this case grunt) generates the directory contents. You could then zip them up and upload them to AMO.

├── Gruntfile.js              
├── package.json               
├──────────────────────────────── dist
│                                 ├── bootstrap.js
│                                 ├── install.rdf
│                                 ├── package.json
├── data                          ├── data
│   ├── js                        │   ├── js
│   │   ├── dialog.js             │   │   ├── dialog.min.js
│   │   └── popup.js              │   │   └── popup.min.js
│   ├── scss                      │   ├── css
│   │   ├── popup.scss            │   │   ├── popup.css
│   │   ├── dialog.scss           │   │   └── dialog.scss
│   │   └── common.scss           │   │
│   ├── html                      │   ├── html
│   │   ├── dialog.html           │   │   ├── dialog.html
│   │   └── popup.html            │   │   └── popup.html
│   ├── vendor                    │   ├── vendor
│   │   └── jquery-2.1.4.min.js   │   │   └── jquery-2.1.4.min.js
│   └── images                    │   └── images
│       └── logo.png              │       └── logo.png
├── lib                           ├── lib
│   └── main.js                   │   └── main.js
└── locale                        └── locale
    └──              └──


A few more tips

If you can avoid obfuscating or minifying code, your review can be done by any reviewer. Should you still need to attach sources, make sure you provide clear instructions so that our admin reviewers can handle your add-on quickly. Responding to questions quickly and using well-known obfuscation tools also improve review time.

Some last words

While our reviewers, both volunteer and staff, review add-ons around the clock, there may be times when it just takes longer. This can be due to anything from Firefox releases and major product changes, to holiday seasons.

I hope you’ve found this post helpful. There’s a lot to remember, but after you’ve done this once or twice you should get the hang of it. If you’d like a page to bookmark that contains this information and some more details on the topic, please head over to our new article on MDN.

If you also have tips to share, or questions on this topic, please post in our forums. Also, if you ever want to sit with developers on the other side of the table, perhaps consider applying to become an add-on reviewer?

Add-on Compatibility for Firefox 46

Jorge Villalobos


Firefox 46 will be released on April 19th 26th. Here’s the list of changes that went into this version that can affect add-on compatibility. There is more information available in Firefox 46 for Developers, so you should also give it a look.



  • Firefox is currently enforcing add-on signing, with a preference to override it. Firefox 46 will remove the preference entirely , which means your add-on will need to be signed in order to run in release versions of Firefox. You can read about your options here.


Let me know in the comments if there’s anything missing or incorrect on these lists. If your add-on breaks on Firefox 46, I’d like to know.

The automatic compatibility validation and upgrade for add-ons on AMO will happen in a few weeks (the one for Firefox 45 is still pending), so keep an eye on your email if you have an add-on listed on our site with its compatibility set to Firefox 45.

Add-ons Update – Week of 2016/02/17

Jorge Villalobos

I post these updates every 3 weeks to inform add-on developers about the status of the review queues, add-on compatibility, and other happenings in the add-ons world.

The Review Queues

In the past 3 weeks, 1197 add-ons were reviewed:

  • 1000 (84%) were reviewed in less than 5 days.
  • 54 (5%) were reviewed between 5 and 10 days.
  • 143 (12%) were reviewed after more than 10 days.

There are 90 listed add-ons awaiting review.

Thanks to our volunteer team, and the addition of Philipp Kewisch as a new admin reviewer, the review queues are looking great and have a good shot of staying that way.

If you’re an add-on developer and are looking for contribution opportunities, please consider joining us. Add-on reviewers get invited to Mozilla events and earn cool gear with their work. Visit our wiki page for more information.

Firefox Accounts

Firefox Accounts is now live on AMO. Next time you log in, you’ll be prompted to migrate your account. If you have any problems with this process, please post in the forum thread.

Firefox 45 Compatibility

This compatibility blog post is up. The bulk compatibility validation will be run in the coming weeks.

As always, we recommend that you test your add-ons on Beta and Firefox Developer Edition to make sure that they continue to work correctly. End users can install the Add-on Compatibility Reporter to identify and report any add-ons that aren’t working anymore.

Extension Signing

The wiki page on Extension Signing has information about the timeline, as well as responses to some frequently asked questions. The current plan is to remove the signing override preference in Firefox 46 (updated from the previous deadline of Firefox 44).


Electrolysis, also known as e10s, is the next major compatibility change coming to Firefox. Firefox will run on multiple processes now, running content code in a different process than browser code.

This is the time to test your add-ons and make sure they continue working in Firefox. We’re holding regular office hours to help you work on your add-ons, so please drop in on Tuesdays and chat with us!


We’re working on the new WebExtensions API, and we recommend that you start looking into it for your add-ons. You can track progress of its development in

Style Refresh for (AMO)

Markus Jaritz


AMO is the central hub for developers to distribute their add-ons, and for users to discover them. It’s a workhorse of a site, serving as a publishing platform, online community, and marketplace where over 1 million add-ons are downloaded each month.

The current design has been in place since September 2011, with only minor design changes since. We’ve begun overhauling the entire site to modernize it and make it more reliable, but in the meantime we’ve done a quick visual refresh to bridge the gap until we finish the transformation.

The following design is scheduled to debut in Firefox 48, and will remain in place until the larger overhaul is complete:

Screenshot of the AMO Style Refresh 2016 - this new look will be coming soon

Screenshot of the AMO Style Refresh – coming soon

We started this project by tweaking the existing CSS using the Firefox Page Inspector. This is quite easy and got us visible results for every adjustment we made. Every change we liked was then recorded in a userstyle using Stylish. Adapting style-elements from the Firefox for iOS website, this resulted in AMO looking more modern within hours.

screenshot comparing AMO Style in 2011 and 2016

Comparison of AMO style in 2011 and January 2016

This is the first of many improvements that we will bring to the user experience of the add-on ecosystem. Many of them will take some time to be created and implemented, but they will all  have a strong focus on its users—both the developers of add-ons and the people using them.

For a preview of the new look, you can install this userstyle.

Hi, I’m Your New AMO Editor

Scott DeVaney


jetpackYou may have wondered who this “Scott DeVaney” is who posted February’s featured add-ons. Well it’s me. I just recently joined AMO as your new Editorial & Campaign Manager. But I’m not new to Mozilla; I’ve spent the past couple years managing editorial for Firefox Marketplace.

This is an exciting deal, because my job will be to not only maintain the community-driven editorial processes we have in place today, but to grow the program and build new endeavors designed to introduce even more Firefox users to the wonders of add-ons.

In terms of background, I’ve been editorializing digital content since 1999 when I got my first internet job as a video game editor for the now-dead That led to other editorial gigs at DailyRadar, AtomFilms, Shockwave, Comedy Central, and iTunes (before all that I spent a couple years working as a TV production grunt where my claim to fame is breaking up a cast brawl on the set of Saved by the Bell—The New Class; but that’s a story for a different blog.)

I’m sdevaney on IRC, so don’t be a stranger.

Add-on Compatibility for Firefox 45

Jorge Villalobos


Firefox 45 will be released on March 8th. Here’s the list of changes that went into this version that can affect add-on compatibility. There is more information available in Firefox 45 for Developers, so you should also give it a look.





  • Firefox is currently enforcing add-on signing, with a preference to override it. Firefox 46 will remove the preference entirely , which means your add-on will need to be signed in order to run in release versions of Firefox. You can read about your options here.


  • Support a simplified JSON add-on update protocol. Firefox now supports a JSON update file for add-ons that manage their own automatic updates, as an alternative to the existing XML format. For new add-ons, we suggest using the JSON format. You shouldn’t immediately switch for older add-ons until most of your users are on 45 and later.

Let me know in the comments if there’s anything missing or incorrect on these lists. If your add-on breaks on Firefox 45, I’d like to know.

The automatic compatibility validation and upgrade for add-ons on AMO will happen in the coming weeks, so keep an eye on your email if you have an add-on listed on our site with its compatibility set to Firefox 44.

February 2016 Featured Add-ons

Scott DeVaney


Pick of the Month: Proxy Switcher

by rNeomy
Access all of Firefox’s proxy settings right from the toolbar panel.

“Exactly what I need to switch on the fly from Uni/Work to home.”

Featured: cyscon Security Shield

by patugo GmbH
Cybercrime protection against botnets, malvertising, data breaches, phishing, and malware.

“The plugin hasn’t slowed down my system in any way. Was especially impressed with the Breach notification feature—pretty sure that doesn’t exist anywhere else.”

Featured: Decentraleyes

by Thomas Rientjes
Evade ad tracking without breaking the websites you visit. Decentraleyes works great with other content blockers.

“I’m using it in combination with uBlock Origin as a perfect complement.”

Featured: VimFx

by akhodakivkiy, lydell
Reduce mouse usage with these Vim-style keyboard shortcuts for browsing and navigation.

“It’s simple and the keybindings are working very well. Nice work!!”

Featured: Saved Password Editor

by Daniel Dawson
Adds the ability to create and edit entries in the password manager.

“Makes it very easy to login to any sight, saves the time of manually typing everything in.”

Nominate your favorite add-ons

Featured add-ons are selected by a community board made up of add-on developers, users, and fans. Board members change every six months, so there’s always an opportunity to participate. Stayed tuned to this blog for the next call for applications.

If you’d like to nominate an add-on for featuring, please send it to for the board’s consideration. We welcome you to submit your own add-on!