Manifest V3 & Manifest V2 (March 2024 update)

Calling all extension developers! With Manifest V3 picking up steam again, we wanted to provide some visibility into our current plans as a lot has happened since we published our last update.

Back in 2022 we released our initial implementation of MV3, the latest version of the extensions platform, in Firefox. Since then, we have been hard at work collaborating with other browser vendors and community members in the W3C WebExtensions Community Group (WECG). Our shared goals were to improve extension APIs while addressing cross browser compatibility. That collaboration has yielded some great results to date and we’re proud to say our participation has been instrumental in shaping and designing those APIs to ensure broader applicability across browsers.

We continue to support DOM-based background scripts in the form of Event pages, and the blocking webRequest feature, as explained in our previous blog post. Chrome’s version of MV3 requires service worker-based background scripts, which we do not support yet. However, an extension can specify both and have it work in Chrome 121+ and Firefox 121+. Support for Event pages, along with support for blocking webRequest, is a divergence from Chrome that enables use cases that are not covered by Chrome’s MV3 implementation.

Well what’s happening with MV2 you ask? Great question – in case you missed it, Google announced late last year their plans to resume their MV2 deprecation schedule. Firefox, however, has no plans to deprecate MV2 and will continue to support MV2 extensions for the foreseeable future. And even if we re-evaluate this decision at some point down the road, we anticipate providing a notice of at least 12 months for developers to adjust accordingly and not feel rushed.

As our plans solidify, future updates around our MV3 efforts will be shared via this blog. We are loosely targeting our next update after the conclusion of the upcoming WECG meeting at the Apple offices in San Diego. For more information on adopting MV3, please refer to our migration guide. Another great resource worth checking out is the recent FOSDEM presentation a couple team members delivered, Firefox, Android, and Cross-browser WebExtensions in 2024.

If you have questions, concerns or feedback on Manifest V3 we would love to hear from you in the comments section below or if you prefer, drop us an email.

9 comments on “Manifest V3 & Manifest V2 (March 2024 update)”

  1. Mohamed wrote on

    The main concern for almost everyone with MV3 is how it affects capabilities of add-ons such as ad blockers. Both add-on developers and users will not prioritise cross-browser compatibility over user freedom if it means weakening the latter. So, if you please highlight that when you talk about Firefox’s implementation, it would be appreciated.

  2. Brad wrote on

    I switched to Firefox one & an half years ago because of impending MV3 in Chromium browsers and I hope you continue to support MV2 and/or MV3 with webRequest Blocking. I hope Firefox can gain users from those who know what this issue is and from those who can be made to understand the same. I like Firefox a lot, especially it’s capability to customize it appearance.

  3. Steve Ford wrote on

    All these elaborate write-ups extolling the virtues of Firefox and Mozilla on their coveted extensions, yet there is no means of feedback if something is not working or inaccessible. And with no obvious button or link to readily get hold of anyone to try and get something fixed. If there are any means of getting something fixed…it is most always tucked way back and beneath piles of accolades to the developers, with little to no thoughts about how the end user is faring. It seems that all the developers are interested in is obtaining some remuneration or big bonus for their work. There it all ends.

    It would be great if someone took an interest in seeing that these various infractions and aka: bugs were rectified, and would send me a reply…..that would be great, but I am certainly not holding my breath waiting for that to happen. Mozilla and Firefox are way too busy being in bed together that they really could give a rats ass if anything was fixed or not.

    1. Edward Sullivan wrote on

      I apologize in advance if I am interpreting your comments incorrectly.

      Regarding providing feedback – are you referring to browser feedback or extension feedback? Extension feedback should be sent to the developer of the extension. Most extensions have a link on their listing page for support (in the left rail under the More Information section; example: For browser feedback, you may submit at:

  4. Robert wrote on

    Mozilla should continue V2 forever for following reasons.

    1. Many Chrome users will switch to Firefox to keep using V2 add-ons, improving the browser usage globally.
    2. Some add-ons, which uses in corporation only, are not maintainable due to the developer left. RemovingV2 support will make the corporation switch to other solution swiftly. Just like Win7/WinXP, you really should not break people’s work.
    3. Similar to many semi-abandoned extension developers, who ghosted. It just works, and I expect you to keep it this way.
    4. Converting V2 to V3 is not a simple task, in some cases it needs total rewrite by skilled professional and long time, which I cannot afford at the moment due to the world poverty.
    5. Also, some add-ons cannot be converted due to the lack of support (e.g. missing API on V3)

    In summary, you really should keep V2 forever. The world will not fogive firefox when you ditch it.
    If you really want Firefox to be number 1, you do above.

    P.S. Please stop resticting users from installing XPI file on the mobile device I own. I want to do what I want, and it is not your decision.

    1. Edward Sullivan wrote on

      Thank you for your feedback.

      As mentioned in the post, we will be keeping MV2 support for the foreseeable future.

      Generally speaking though, it’s difficult to commit to indefinite support since we cannot foresee what may happen a year or 10 down the road. However, we can commit to ensuring that if we do need to deprecate MV2 in the future, we will make every effort possible to provide ample warning and minimize the impact on our developers and users.

  5. Francisco Luz wrote on

    From Alta Floresta, MT, Brazil here. Thank you Edward very much for the update. You guys from Mozzilla are doing a fantastic work.

    Over here in brazil the use of certificates to login into a variety of government agencies and services is widespread. Employees of accounting firms have a though time maintaining a large catalog of client’s certificates installed in their machines. To solve that I am writing an extension that intercepts all login requests and send them to the local network server. The local server has all the client’s certificates so can impersonates the browser. The server then do the login via curl, grab the cookies and send them back to be injected into the local user browser.

    Initially I started development with MV3 but the webRequest fiasco was a bummer. I switched over to MV2 and everyone in the office will be required to use firefox. I am very happy to hear that MV2, which works just fine, is gonna be around in firefox.

  6. Olivier wrote on

    Hi Edward,

    I’m the developer of the extension named Context Search which I started developing when Firefox adopted web extensions. I have spent hundreds of hours developing the extension which now counts several thousands of lines of code. Unfortunately, it hasn’t been financially rewarding as I’ve learnt that, if something is provided for free, then users will very rarely make a donation. They will however complain when things don’t work, sometimes by providing poor reviews. But, that’s besides the point I want to make! In the recent past, I have looked into migrating the extension to Chrome and thereby adopting MV3. However, I quickly came to realize that I would have to rewrite almost all the code to move to service workers and get rid of global variables. Therefore, with so many lines of code, without some AI automation that would help with the task, if Mozilla decided to abandon MV2, then it would simply be the end of Context Search and I will have wasted my time.

    Thanks in advance for your consideration.

  7. Tommy wrote on

    We’ve had to drop support for Firefox because of too many things not yet implemented or implemented differently in Firefox vs. Chrome/Edge. Some things that come to mind:

    – service worker
    – offsceen permission
    – userScripts permission