Add-on Compatibility for Firefox 54

If you haven’t yet, please read our roadmap to Firefox 57.

Firefox 54 will be released on June 13th. Here’s the list of changes that went into this version that can affect add-on compatibility. There is more information available in Firefox 54 for Developers, so you should also give it a look.


  • Remove -moz-appearance. This doesn’t apply to CSS sheets loaded using a chrome:// URL, but it does affect inline CSS styles in XUL and JavaScript code.

XPCOM and Modules


Let me know in the comments if there’s anything missing or incorrect on these lists. If your add-on breaks on Firefox 54, I’d like to know.

The automatic compatibility validation and upgrade for add-ons on AMO will happen in a few weeks, so keep an eye on your email if you have an add-on listed on our site with its compatibility set to Firefox 53.

8 responses

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  1. Kees wrote on :

    Is the WebExtension feature set of this version already on a proper level (i.e. a level where the features of the top 25 [and preferably the top 50-100] most popular add-ons are implemented *with version 54*)??? If it is not then I strongly suggest/recommend/ask for a change in plan related to deprecating the XPCOM based add-ons.

    In that case I (again) suggest to extend the support of XPCOM based add-ons to at least the next ESR (It is still *VERY* surprising that a major change like this one is not aligned to be effective just after an ESR edition) .

    N.B. Is it possible to explain *why* a major change like this is not aligned to be just after an ESR version? As that is a much more sensible version than doing it about 3 months before the next ESR….


    1. Jorge Villalobos wrote on :

      You can find the current plan on this blog post. We don’t intend to change it, and there’s plenty of discussion around it in the comments.


      1. Kees wrote on :

        I know of this plan, however this still doesn’t address the question why it is not aligned to be after an ESR…

        And it also doesn’t answer the question related to the feature-parity.

        When the feature set of WebExtensions is not the same as the top 25 most popular XPCOM add-ons then there is a major regression related to add-ons which isn’t a logical action in a version just before the next ESR.


        1. Jorge Villalobos wrote on :

          Quick summary of what’s already been discussed on that post and the comments:

          1) Starting with 57, many things will break that will also break add-ons. Most add-ons that aren’t WebExtensions will be broken regardless. Aligning with ESR is not a goal.
          2) WebExtensions will never do everything XPCOM does, so feature parity is not a goal. Some top add-ons can’t be completely ported (DownThemAll and Firebug come to mind) and we’re accepting that risk.


          1. Arnaud wrote on :

            Hello Jorge,

            I don’t want to troll (and you don’t need to waste time answering me), but I wouldn’t call the second item a “risk”. It’s more of a regression. The risk are : bad buzz (already there), unhappy users and loss of market share.

            Don’t get me wrong, I love WebExtensions and I want Firefox to improve quickly. I understand that sometime you need to make sacrifices (in french we say “lâcher du lest”, literaly “to dump ballast”, it’s an hot-air ballon analogy). But it looks like communication on this subject is far from perfect.

          2. kup wrote on :

            Interesting words: “we’re accepting that risk”. Are you trying to convince or to soothe yourselves? WebExtensions is a path to nowhere, but Mozilla is too blind to see it. I know that my words change nothing, but, at last, stop telling lies to community, guys. Please.

  2. Juraj M. wrote on :

    @kup I understand your frustration – spending so much time learning some API that is now gonna be obsolete. But now there will be a common standard that allows you to port your extension to all popular browsers including Edge with minimum or zero effort.


  3. Robert Ab wrote on :

    When it will be possible to watch 1080p Netflix movies in Firefox? This is especially important for Windows 7 users, where all browsers support 720p:
    As you will notice Firefox supports only 720p (in all OS).



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