It's not a huge leap to see how the same could apply to add-ons too, it frequently does even on desktop. It would be many times more likely for the new android Firefox, hence the existence of the allowlist. Not to mention that some of the restrictions aren't artificial at all.
As for support, a) we'd like to support all of our users, and b) it often takes a lot of support time until you establish that an add-on or hidden preference is responsible.
> Not to mention that some of the restrictions aren't artificial at all.
Such as?
> a) we'd like to support all of our users
Only what the users would like matters. Giving them the choice between being installing what they want and getting support is strictly better than a forced whitelist.
> b) it often takes a lot of support time until you establish that an add-on or hidden preference is responsible.
For extensions, as I understand it not all the APIs are implemented yet for geckoview. Not my area though so can't provide more details. For about:config, again lots of the preferences don't make sense for geckoview, or can even break it completely.
> Giving them the choice between being installing what they want and getting support is strictly better than a forced whitelist.
For you perhaps. But for many users having a working browser is more important. Users don't deliberately break their browsers, yet it happens all of the time. I believe (and I'm speaking for just myself here, not Mozilla) that finding a balance between allowing users to install/tweak many things whilst ensuring a usable browser is better.
> Then check for that first.
Sure we could immediately check if users have any addons or prefs set, and just ignore them if so. But that would let many genuine bugs slip through, not to mention not be very nice to those people.
As for support, a) we'd like to support all of our users, and b) it often takes a lot of support time until you establish that an add-on or hidden preference is responsible.