And I can confirm that hacking /usr/lib/firefox/omni.ja to change MOZ_ALLOW_ADDON_SIDELOAD to true "fixes" the problem.
-- You received this bug notification because you are a member of Desktop Packages, which is subscribed to firefox in Ubuntu. https://bugs.launchpad.net/bugs/1866059 Title: firefox-locale-* packages do not enable localization => post-install localization is not complete Status in firefox package in Ubuntu: Confirmed Bug description: On 2020-03-03 I installed a Focal system from the latest ISO image and chose the Italian localization at install time. The localization setting worked as expected, but not for Firefox: its interface is still in English. No "Italian" option shows up in the 'Preferences -> Language' menu (the menu is empty). The firefox-locale-it package is correctly installed. I tried installing firefox-locale-fr and restart Firefox, but I still got no French option in the Language menu. On the other hand letting Firefox download the language pack itself *does* work. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/firefox/+bug/1866059/+subscriptions -- Mailing list: https://launchpad.net/~desktop-packages Post to : desktop-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~desktop-packages More help : https://help.launchpad.net/ListHelp