[Blog post] Manifest V3 signing available November 21 on Firefox Nightly

We are excited to announce that you can sign your MV3 extensions starting November 21st in AMO and that MV3 will be available in Firefox 109 (release January 17th 2023).

Read more about our vision for MV3, the timeline moving forward and what you can do now to transition your extensions to MV3 from our blog post:


Thanks for adding the Manifest V3 support! I guess my situation is less common than for most devs, but I have a V3-only extension which previously only supported Chrome-based browsers. (My experience with V3 has only been positive, starting from a new project a few months ago.) I was waiting for Firefox to add V3 support before supporting Firefox, as I didn’t want to maintain a V2 and V3 version.

I was able to add support for Firefox relatively easily thanks to the new Manifest V3 support, and I got my extension onto AMO ready for 109’s release tomorrow — looking forward to announcing Firefox support.

There were a few general browser differences to handle (like different clipboard APIs), but nothing major. The background page vs service worker difference was the main thing directly related to extension APIs. But my service worker code worked as a background page, so I could handle the split by having my build process generate separate (mostly identical) builds for Chrome and Firefox, with the Firefox version including browser_specific_settings and swapping background.service_worker for background.scripts.

These were all the changes I made: https://github.com/h4l/headgear/pull/19/commits

Something that’s not quite clear to me is whether strict_min_version needs to be set to 109.0 for a V3 extension, or whether the manifest’s version being 3 is enough. The “Distribute Manifest V2 and V3 extensions” page seemed to suggest it should be used, so I included it to be on the safe side.

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You should use strict_min_version, otherwise people running older versions, like Firefox ESR 102, will be able to install it as well but it won’t work for them. So they may complain and leave negative reviews.
You can’t break anything by including it. And you can also change it after the release - from the Developer hub:

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Good to know, thanks @juraj.masiar.