It would be good if they explained this in their documentation. But I think you summed it up in your own message:
> […] you can either have a browser that doesn't catastrophically break every few updates; or you can have the freedom to install whatever addons you like […]
I think they don't want malicious and abandoned extensions to taint the Firefox experience. Users will only see "Firefox is broken" and not realize that it's caused by the extensions they installed.
I've been using Kiwi browser on Android for years. It supports like 80% of chrome extensions, never breaks on updates. The only major issue is that extension settings pages are rarely optimized for mobile.
They could trivially bury full add-on market access under 5 scary models and a password or something, but instead they use an absurdly cumbersome mechanism.
Recommended extensions, those that are currently available are vetted by Mozilla staff, not only for safety, but for utility and alignment with Mozilla's goals. These require no warnings or disclaimers.
Community approved extensions would be on AMO and approved by staff-selected community members for safety and policy compliance. No warnings, but a link/checkbox/toggle at the bottom of the extensions page.
All of AMO - this should need a toggle to turn on, and a warning that extensions have not been tested and could be unstable or malicious with a second checkbox to acknowledge.
Local install - this should be buried in the settings and called something like "I am an extension developer". Turning it on should pop up an additional warning about other peoples' code being dangerous. Actually installing an extension should require separate use of a file manager or command line, and then enabling it inside the Firefox UI.
The current approach reminds me of Apple's app store, except it's much harder to get on the recommended list than to get an iOS app approved.
There are only like 15 of us using Firefox mobile. It is safe to say that if you are using Firefox mobile, you are technically savvy enough to go "Ah, I installed some extensions and now Firefox crashes a lot".
Let extensions claim whether they work on mobile or not, and open the flood gates.
> […] you can either have a browser that doesn't catastrophically break every few updates; or you can have the freedom to install whatever addons you like […]
I think they don't want malicious and abandoned extensions to taint the Firefox experience. Users will only see "Firefox is broken" and not realize that it's caused by the extensions they installed.