Just a couple of eslint issues with those bundles not being available anymore.
https://treeherder.mozilla.org/logviewer?job_id=416788663&repo=comm-central&lineNumber=260

Pushed by alessandro@thunderbird.net:
https://hg.mozilla.org/comm-central/rev/7e30e71042eb
Port Bug 1793557: Use our own addons.properties and brand.properties in aboutAddonsExtra.js. r=mkmelin DONTBUILD

There's more work to be ported. I'll look at that now.

(In reply to Magnus Melin [:mkmelin] from comment #3)

There's more work to be ported. I'll look at that now.

See https://phabricator.services.mozilla.com/D158663#inline-984230 and the "Thunderbird" part of the comment. The code suggested in that comment has been adopted and can be viewed at https://searchfox.org/mozilla-central/source/toolkit/components/extensions/ExtensionPermissionMessages.sys.mjs . Feel free to tag me for review or feedback in a patch if you need more help.

Thanks. We unfortunately have a whole heap of semi-forked code that need to be adjusted/synced. And strings that need to be moved to Fluent to operate without hacks at least. I think.

Thunderbird shouldn't be special cased here. This is testing toolkit behavior.

This is syncing a lot of semi-forked code.
Much of the duplicated strings from Firefox are not needed anymore. Still need to look at Fluent migrations.

Nothing more permantent than a temporary fix...

https://hg.mozilla.org/mozilla-central/rev/d49f009b89ad

Pushed by geoff@darktrojan.net:
https://hg.mozilla.org/comm-central/rev/1a55e2c03721
Port Convert ExtensionsUI.jsm strings to Fluent to Thunderbird. r=john.bieling
https://hg.mozilla.org/comm-central/rev/334119edb763
Remove unused code in ExtensionsUI.jsm. r=mkmelin