I am one of the developers of the Censor Tracker add-on, which is listed on Mozilla’s add-on repository. We recently noticed that our add-on is now unavailable in Russia, despite being developed specifically to circumvent censorship in Russia. We have not changed any visibility settings, nor have w...
Not blaming Mozilla for this specifically but since they're architecture is centralized, they are at the whim of centralized governments who want things to be changed.
So by designing systems, where they are the central authority, they are vulnerable to exactly this happening again and again and again
Mozilla centrally signs every add-on—but the add-ons in question are still signed by Mozilla
Mozilla runs a centralized distribution platform but you can self-host your add-on if you want and you have the option to use a custom update URL—the add-ons in question are still hosted by Mozilla, however, they are geo-blocked in the country that counts
Tbf, it's probably to prevent Russia from carpet banning Mozilla services and products. They might just do that, create a new foundation called "MegaLizard", with the browser "Greyhound"...
That being said, unlike with Chrome, installing third party extensions for Firefox outside the extension store is fairly uncomplicated.