Of course, Firefox also broke extensions on Android for several years, during which I mostly used a lightly tweaked Chromium build called Kiwi Browser.
Hmm, I didn’t really notice that. (I’m using Fennec F-Droid though, but it’s pretty close to the official Firefox build, with only a few minor tweaks.)
Could you tell me more about what was broken for you?
Third party builds differed, of course.
Personally, I’d just allow installing any extensions (from AMO at least) and put a big scary warning that this is unsupported (which was the reason they gave for the whitelist approach).
Firefox on Android still doesn't look like it has the ability to save pages. Chrome and Kiwi both have this feature, and Firefox used to have it via extension that triggered built-in, but unexposed, functionality.
I think Brave could be a pioneer here and add a further point of differentiation by allowing extensions.
Also on iOS, Orion supports both Chrome and Firefox extensions.
The author is playing with his own bookmarklets and extensions that will never be part of the browser, as it serves his own needs, not someone else’s.
For the browser to act as the user agent, it needs to be scriptable.