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Manifest v3 signing available November 21 on Firefox Nightly

Starting November 21, 2022 add-on developers are welcome to upload their Firefox Manifest version 3 (MV3) compatible extensions to (AMO) and have them signed as MV3 extensions. Getting an early jump on MV3 signing enables you to begin testing your extension’s future functionality on Nightly to ensure a smooth eventual transition to MV3 in Firefox.

To be clear, Firefox will continue to support MV2 extensions for the foreseeable future, even as we welcome MV3 extensions in the release to general availability in Firefox 109 (January 17, 2023). Our goal has been to ensure a seamless transition from MV2 to MV3 for extension developers. Taking a gradual approach and gathering feedback as MV3 matures, we anticipate opportunities will emerge over time to modify our initial MV3 offering. In these instances, we intend to take the time necessary to make informed decisions about our approach.

Towards the end of 2023 — once we’ve had time to evaluate and assess MV3’s rollout (including identifying important MV2 use cases that will persist into MV3) — we’ll decide on an appropriate timeframe to deprecate MV2. Once this timeframe is established, we’ll communicate MV2’s closure process with advance notice. For now, please see this guide for supporting both MV2 and MV3 versions of your extension on AMO.

Mozilla’s vision for Firefox MV3

Firefox MV3 offers simplified and consolidated APIs, enhanced security and privacy mechanisms, and functionality to better support mobile platforms. As we continue to collaborate with other browser vendors and the developer community to shape MV3, we recognize cross-browser compatibility as a fundamental consideration. That said, we’re also implementing distinct elements to suit Firefox’s product and community needs. We want to give extension developers creative flexibility and choice, while ensuring users maintain access to the highest standards of extension customization and security. Firefox MV3 stands apart from other iterations of MV3 in two critical ways:

  1. While other browser vendors introduced declarativeNetRequest (DNR) in favor of blocking Web Request in MV3, Firefox MV3 continues to support blocking Web Request and will support a compatible version of DNR in the future. We believe blocking Web Request is more flexible than DNR, thus allowing for more creative use cases in content blockers and other privacy and security extensions. However, DNR also has important performance and compatibility characteristics we want to support.
  2. Firefox MV3 offers Event Pages as the background script in lieu of service workers, though we plan to support service workers in the future for compatibility. Event Pages offer benefits like DOM and Web APIs that aren’t available to service workers, while also generally providing a simpler migration path.

Over subsequent releases next year, we’ll continue to expand Firefox MV3 compatibility.

MV3 also ushers an exciting user interface change in the form of the new extensions button (already available on Firefox Nightly). This will give users direct control over which extensions can access specific web sites.

The extensions button will give Firefox users direct control over website specific extension permissions.

Users are able to review, grant, or revoke MV3 extension access to any website. MV2 extensions will display in the button interface, but permissions access is unavailable. Please see this post for more information about the new extensions button.

If you’re planning to migrate your MV2 extension to MV3, there are steps you can take today to get started. We always encourage feedback from our developer community, so don’t hesitate to get in touch:

11 comments on “Manifest v3 signing available November 21 on Firefox Nightly”

  1. Juraj M. wrote on

    Is “Service Workers support” planned for the Firefox ESR 115 in the September 2023?
    Saying only “we plan to support service workers in the future” makes me a bit worry 🙂

    1. surtic86 wrote on

      Yes… im waiting on Service Workers since i have already my Extension Implemented with it on Chrome and Safari.

      1. Juha-Matti Santala wrote on

        We hear you! Our team continues working on MV3 and finishing these compatibility features is a focus for us. We don’t however have a date yet for when they would be available.

    2. TranquilMarmot wrote on

      We have a MV3 extension that we’ve released for Chrome that we’re planning on releasing for Firefox soon.

      We actually dynamically generate the manifest with a small node script on build. We have something like this:

      background: FIREFOX
      ? {
      // Firefox doesn’t support `service_worker` yet
      scripts: [“background.js”],
      : {
      service_worker: “background.js”,

      So far, it is working just fine. We’re also using `webextension-polyfill` for all of the browser/extension communication.

  2. Max wrote on

    I am not a fan of a unified extensions button. I like my extensions lined up on the extensions toolbar where I can see them and interface with them and I want them to stay there. If that bar goes away, I will stop updating Firefox at that version. Humbly yours, FF user since FF 31.8.0.

    1. Juha-Matti Santala wrote on

      The toolbar isn’t going away. You will still be able to pin your extensions to the toolbar and interact with them.

      You can have your most used extensions in the toolbar for easy access while having a convenient way to provide permissions for all extensions through the Unified Extensions Button.

  3. Max Galbu wrote on

    > Starting November 21, 2022 add-on developers are welcome to upload their Firefox Manifest version 3 (MV3) compatible extensions to (AMO) and have them signed as MV3 extensions.

    At what time?

    1. Juha-Matti Santala wrote on

      Sorry for the late reply but it’s now available.

  4. Max wrote on

    So, basically, FF doesn’t support mv3 yet… I tried all my extension and no one works, of course I use service worker which google suggest to use and I can’t to make an additional version for FF, so will wait mv3 support and for now will continue to say to my users that FF is delaying mv3 support and they must switch to any chrome browser 🙁

    1. Juha-Matti Santala wrote on

      Hey Max!

      We are encouraging the use of event pages rather than service workers for background pages in MV3 extensions and that’s why that is what we have in the initial launch.

      We’ll be adding features like declarativeNetRequest and support for service workers as we improve the compatibility of our implementation with Chrome’s MV3 implementation.

  5. Horia wrote on

    Can you please provide an option to remove the button from the toolbar? The back and forward buttons can no longer be removed, and now the Unified Extension Button cannot be removed either. I really liked the customization that Firefox provided, allowing a toolbar without clutter, with just the bare minimum: the address bar and the menu button.