Major compatibility changes coming for Firefox 25

We released Firefox 21 just a couple of weeks ago. This means 22 is on Beta, 23 on Aurora and 24 on Nightly. Firefox 25 won’t be released until late October, so we still have a ways to go. However, this is a significant release because 24 is slated to be an Extended Support Release, so some major changes have been pushed after then to minimize any potential impact.

There are two major add-on compatibility changes to look forward to, and I’m giving you this heads up just so that you’re aware and plan ahead. Things might change as we move forward, and I’ll keep you posted about it, but you should definitely check out the Nightly builds in July, or the Aurora builds during the month of August. It’s likely that your add-on will be affected by these or other changes.


Update: as of September 19th, it looks like the Australis update won’t happen until at least Firefox 27.

This is a major theme revamp in Firefox that has been worked on for quite a while. One of its objectives is to simplify the UI, taking add-ons into account.

There are major changes coming to how toolbars work. There is some back and forth going on over the topic of removing the Add-on Bar completely. It doesn’t look like a final decision has been made, but in the best case it will be a harder to find customization target, and it the worst case it will be gone entirely.

The main toolbar will also have a dedicated area for add-on buttons and widgets, and it looks like user-created custom toolbars will also be gone. Overall, you should plan for a minimalistic toolbar UI. While most add-ons do this already, it’s possible that the API to add toolbar buttons will be very different, and there will be changes to be made for all of them.

You can do early testing of the Australis changes by installing the UX Nightly Branch. If you have any feedback from these tests, please share it in the comments below.

Session Restore

Like many other areas of Firefox code, Session Restore is getting the asynchronous treatment to improve its performance. If you look at bug 874381 and its dependencies, there are several changes to this module that will affect add-ons. Particularly, there are many add-ons that rely on private variables (starting with __SS) that will no longer exist.

There’s a list of affected add-ons in this blog post, and some of the developers have already been notified. However, you should check yourself if your add-on relies on any of these private variables and start migrating away from them, since they will be gone in 25.

Once we’re closer to the Firefox 25 release, we will have more information and hopefully better documentation to point you to. For now, I hope this heads up will be useful and you start looking into these big changes that are coming up.

125 comments on “Major compatibility changes coming for Firefox 25”

  1. Chris wrote on

    I found it amusing when a so called UX team says they dont know what to do to please everyone, how about leaving everything the **** alone. ITs like changes are been done to justify their existance.

    So my session restore I rely on is about to break, my status4ever may stop working, I lose my addon bar? Classic toolbar addon I installed to undo lame firefox updates.

    Hang on I worked it out now, these changes are to break addons that restore legayc firefox behaviour, I think the firefox UI team hasnt took too kindly to people making addons that undo their changes so are making new changes to disable these addons.

  2. SaphirJD wrote on

    Minimalistic Design which takes away most customization options. What a wonderful trade….

    Seems Palemoon or Cyberfox are the way to go for more advanced or Power Users, since the Devs of these 2 Forks of Firefox have said that they are not using Australis with its restrictions.

  3. nah wrote on

    It isn’t always the best idea to copy Chrome. Shoving all add-on UI into the navigation bar was never a good idea, and I’d hate to see it happen to Firefox, where lots of add-ons take up more space than a standard button. The navigation bar controls wouldn’t be very usable, especially with non-maximized windows. If you need another Chrome-like feature to do instead of this, I would suggest Electrolysis. Now that would be something.

  4. Allasso Travesser wrote on

    Another change worth mentioning here which may affect some addons such as Find All:

    The Findbar has changed. There is no longer “The” Findbar, contained in browser-bottombox, but each tab now has its own individual Findbar, contained within each notificationbox.

  5. Dom Diesel wrote on

    For all who are not interested in using an upcoming “Mozgoogle Chromefox”:

    Firefox forks which stay Firefox without turning into google 🙂



  6. Firefox user wrote on

    My question to the “genius” who decided this is, why in the name of sanity remove a feature users like that sets the browser apart from competition? Do you really wish so much for your userbase to shrink? I really have to agree with previous poster – this is turning into Mozgoogle Chromefox … and a deficient one at that. If i wanted google chrome, i would install it.

    The fact that users are using the addon bar means it has legitimate purpose. The fact that some users even use status4ever addon just shows that you already made similiar mistake once before.
    Customizability is the thing that made me chose firefox over other browsers. If users want minimalistic interface, they have the option to configure firefox to their liking. Please don’t force your subjective esthetic choice on users who don’t agree with it.

  7. Staritza wrote on

    How can they do this??? It is utterly insane, and is bound to see a massive migration to Cyberfox. Looks like RIP Firefox, and we will bitterly miss you.

  8. Mart wrote on

    The session restore overhaul is actually very important and I understand it will be carried out incrementally over subsequent browser releases to make the feature more robust and less prone to failure.

    The importance of this overhaul is that it allows to reduce latency (=memory consumption, processor usage and hard disk usage, which in some cases is particularly heavy) and reduce the likelihood of data loss.

    1. clas wrote on

      Yeah, I am tired of the too fast changes for what seems is just change sake. As far as memory useage, I just use Firemin and my memory useage goes from 400,000+ to about 10,000 and runs smooth as can be. I wont be downgrading to the new australis version and like the version I am running with all my bells and whistles running perfectly. Like other posters have said, If I wanted Chrome, I would use it. I have figured Firefox out and like what I have…I dont need to learn it all over again so often. I know the developers are trying to justify their jobs but change for change sake is Microsofts ballywick. It seems Microsoft doesnt listen and now Mozilla isnt listening either.

      1. David wrote on

        what is Firemen? add-on?

  9. Richard wrote on


    Please listen to our users. We don’t want you to remove customization options. Customization and power is the reason why we continue to use your product. Leave the firefox UI alone. It’s already “modern” enough. Opera decided to do the same thing, and now look and at them. They now have a crappy browser that doesn’t even have the most basic customization features. I hope that you guys will read mine, and everybody else’s comment and decide to undo this “minimization” before it’s too late .

  10. Seb wrote on

    I know a simple solution for you, go to google and say to them you do not take their money anymore because you want again to develope your browser like you want to do it.

    Easy solution, you can make it again customizable. Only a blind one does not realize that it is google’s money what makes Mozilla act like Google wants them to do…

    Who pays the bill, decides. So, search another money giver and go away from Google, most simple and effective solution, without Googles direct influence in Mozilla’s decisions, there would be no Australis!

    And eveyone knows that, or do you think the people are so blind to not realize that? 😉

  11. Squuiid wrote on

    Oh man NO. I don’t think Mozilla understands how fragile their user base is. Users will drop their browser in a second if they make changes which permanently restrict or break add-ons.

    For example, if Australis prevents Roomy Bookmarks, ABP and Xmarks from working as well as they do now, I am gone! It’s not as if there aren’t other good options to go to.

    Don’t rock the boat for the sake of it Mozilla. Leave the UX as it is! There is nothing wrong with it.

  12. SaphirJD wrote on

    Exactly why i dropped Firefox in favour of Chromium lately now as final decision. Some people love to have Basic Customizations inside the Browser and not using more unsecure third party solutions for that reasons.

    Add-Ons are for features which are useless to have in a Program. But going so far and saying Basic Customization is useless… Boy, You Mozilla guys have a serious mindset problem!

    Think about that, when already users like me who are using Firefox nearly since day one are dropping the Browser in that case.. You can expect to go down in market share quite a bit.

    What makes it different from Opera, they will gain for sure again, because they add stuff back, even on a complete limited engine in terms of customization like Blink now!

  13. metal696heart wrote on

    Dont touch the addons bar! Dont touch the UX just for the sake of changing something!

    For exmple i use bottom tabs (allmost exclusively). This is the main reason why i DONT use Chrome or dervatives. And to use the bottom tabs i need a space between the taskbar and tabs bar. That space is also filled with quick access small buttons from addons: abp, firessh, firebug, dev tools, gmail check, video downloader, picozu and various others.

    Menubar on titlebar near the firefox main button and one main toolbar with buttons, bookmarks, adressbar.

    If you really want to spend some effort on something, speedup javascript rendering and fix the damn memory leaks / memory management.

  14. Roger wrote on

    What I would do with the Addon Bar would make floating and auto hide is to put useful buttons and these are hidden and not take up space. Currently I use a Stylish style that does this, and I must add that for me is perfect. It also acts on the Search Bar, and it appears in the Addon Bar side, left side, and operates independently of the Addon Bar. The Addon Bar appears on the right side, and left the status message. The links appears in the right side of the URL bar.

  15. acturbo wrote on


    Listen carefully … STOP blindly copying Chrome. We use Firefox because of the way it IS/WAS, not because it “almost works like Chrome”. You keep trying to change Firefox into something that resembles the other browsers at the EXPENSE of killing off very useful and critical features.

    Your UX guys should be fired (not the web dev tools, that work is brilliant). The ongoing stupidity of your UX guys leads me to believe they are too junior to understand what’s important to customers. For example, the Find Bar was 100% fine. Now? No. I have a 24″ monitor, i see the Find Bar text input box at the bottom left at 0-1″ mark and the options 15″ away (i measured) on the far bottom right. You have to be an IDIOT to design this. In fact, a TOTAL IDIOT because you actually BROKE a perfectly working design.

    Be unique. The closer you become to Chrome, the easier you make it for people to just SWITCH to Chrome. Your vision is seriously flawed if you think making Firefox look/work like Chrome is in your best interest. The complete opposite is true. Don’t kid yourself, most Firefox people also use Chrome. When developing websites i bounce between Firefox and Chrome … keep this nonsense up and i’ll be using Chrome or something else.

    The Firefox bookmark engine, the add-ons, the ability to customize, and now the web tools … are CORE attributes of Firefox. Change these at your peril.

    WAKE UP.

    1. bua wrote on

      And just to add, the find bar now has, for some bizarre reason, the “previous” and “next” button positions switched. “next” should come first, as it has always done in any sane search feature! Who the heck decides to have “previous” first??

    2. Victor wrote on

      I totally agree with you.

    3. Vince wrote on

      Totally agree. The Find Bar version 24 was perfectly fine. Version 25 is not usable. Angry.

  16. Shannon wrote on

    GARBAGE. If I wanted Chome, I’d INSTALL CHROME. Actually, I HAVE Chrome. I HATE IT. Hence, Firefox. Now, I guess it’s back to IE.

    Smooth move.

  17. alex wrote on

    Would you please stop ignoring the users and leave alone the features that 99% of them use.

    First you got rid of the status bar, even if it was possible to just disable it.
    Thankfully, the Statusbar 4evar” add-on brought it back.

    Now you want to take the add-on bar away?
    We USE it. We LIKE it. We WANT it.

  18. SophieBee wrote on

    Yes, PLEASE LEAVE IT THE HELL ALONE. Every damn time you update it, the thing gets worse. I have to waste ridiculous amounts of time troubleshooting. Today I upgraded to 25 and have had nothing but crashes and hangs and error screens since. It’s a better use of my time to just get IE or Opera configured in a way I can live with and switch to that.

    Why don’t you release a “light” version?

  19. Josh wrote on

    Why would you think of removing the add-on bar? With a simple right-click you can hide it. If it’s aesthetic you’re going for by not having the add-on bar, just make it hidden by default. Then those who like it can simply right-click and enable it. Problem solved.

  20. Melanie wrote on

    It is just awful to be urged to open the Findbar in EVERY tab 🙁
    And there is no way to change it. I would like to have the opportunity to use it the way it was before. Is that so difficult to let people choose in the options?

    1. MSP wrote on

      Seconded! I regularly search across multiple tabs for the same phrase. Now I have to keep entering the same search string for every tab! Madness! How do I get the previous functionality back please? Is there something in about:config?

  21. Cuholvke wrote on

    I’m a designer myself and after looking at that UI I can tell right away that there are no designers in the Mozilla team… hell, they’re just a bunch of lazy slugs relieving themselves of design work making these minimalist shits. Theres nothing worst for a browser user than that, between having to go to the left for the back button, to the right of the address bar to try and hit that microscopic reload button, having to pass over your handful toolbars AND address bar to get to the navigation tabs… ETC… every time I get these stupid updates I spend HOURS, if not DAYS, looking for solutions for things that were not broken before, right now I’m looking for a way to get back de find bar behaviour, I do search words in multiple tabs, now I have to rewrite my search for every fucking tab, that is plain brainless.

  22. MSP wrote on

    I think the people responsible for these changes for the sake of it need to go back and read this page

    “One of the best things about Firefox is that you can completely customize it to fit how you work”

    Ring any bells?

  23. interlist wrote on

    I agree with the findbar being gofoo-ed up.

    Splitting functionality left/right is poor design for the sake of what? Esthetics?

    I do a search, type in the text, find it and then have to move my mouse several inches to close the bar to reclaim screen space? Yipes, who thought that a good idea?

    1. interlist wrote on

      I forgot – also the find bar options/etc. are separated too. Very inconvenient.

      Show me the user feedback survey with the positive response for these changes. From a non-biased sample of general Firefox users. Who is proposing/approving these changes? What methodology are you using?

      1. Jorge Villalobos wrote on

        Most discussions about Firefox feature development happens in the firefox-dev group.

        1. interlist wrote on

          Thanks Jorge, perhaps I should visit there more often.

          Thanks also Amy, but I found an acceptable fix via some CSS code I can run with Stylish.

          It’s discussed here –

          The only thing it doesn’t do is switch the “find next” “find previous” buttons, which I would prefer reversed.

          Searching the web I see that there are many of us immediately hit by this change.

          OK thanks again all.

    2. Amy Tsay wrote on

      Hi interlist, have you given Fastest Search a try?

  24. Jorge Villalobos wrote on

    For those of you looking to recover or enhance your tab search experience, I would recommend trying the Fastest Search add-on. It’s not the same as the old behavior, but it’s probably a good substitute.

  25. DanA wrote on

    This is too much. Reverted to Firefox 24. I’ve been holding out for years, but now seriously considering switching over to Chrome.

  26. Will Sunfire wrote on

    Not at all interested in using a Google colony product. In that case i can also use Chromium. How about stop following trends, making own trends again and break free of Google which controlls you to the bone?

    Or are you so much dependent on google these days? Do you really not understand that it is better to stand on your own again with making own dedicisons instead of letting others decide what you should implement (more similiar to chrome for making it easier for people to switch to Google) and remove (customization)?

    Mozilla does not at all understand the concept hat you only can earn something if you give something! Stop become like Google and go your own way again, you guys have lost it bigtime!

  27. Bob wrote on

    It’s purty,(sic) but that’s about it. I want my addon toolbar back. My weather is now gone and the upper right of the browser is waaaaay to cluttered and some of my addons aren’t visible anymore. The classic toolbar addon which was supposed to bring back the addon bar, now doesn’t. They removed that option. HATE IT!!
    I’ve been doing nightly for a couple of years, time to find a branch that keeps my stuff visible. I don’t give a rat’s A$$ about the browser looking good on a tablet. I want it to be functional on my computer, didn’t learn anything from the Windows 8 debacle????? You don’t build one for all. Or if you do, make it easy to customize the way we like it…. Can’t be that hard.

  28. Sergej wrote on

    I’m using Firefox since version 1.5. And I also use Chrome. Now I will use Chrome only – because I don’t need two Chromes.

  29. Guru Dev wrote on

    Dumping FireFox. <- here is your minimalist message. Thanks.

    Checking out Avant Browser

    Because some day Palemoon and CyberFox would also be arm-twisted into minimalism.

    Good for Mozilla with minimalistic browser they will need fewer developers and employees. Way to go!

  30. diarbe wrote on

    Yahoo steals my start page continuously. Why does Firefox put attention on such pointless things when there are screaming error and inadequacy holes that drive users loopy. Startpage and search engine hijacking is STILL going on with ridiculous unworkable advice given by people you cant reach out and throttle. Is it all just going to go on like this on this stupid planet for years and years till I drop dead?

    Oh. It is?? Oh well I support Boycott of all these mad products and urge you to do the same..

    1. Jorge Villalobos wrote on

      Our support site has instructions to deal with situations like the one you describe. We look for add-ons that don’t follow our guidelines, including changing the default search or homepage at unexpected moments, and block them if necessary. If you have more information about how your home page is being altered, I’ll look into it.

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