Firefox moved to multi-process before moving to WebExtensions. You've lost count of how many mass extinctions the Firefox extension has been through, but there were XUL extensions that were updated to be compatible with multi-process, and then later had to be totally rewritten with completely new UIs when XUL was killed. And the usability hit that extensions like AdBlock Plus and NoScript suffered was crippling, even if it wasn't quite as bad as MV3, and NoScript lost features that went beyond just UI.
> Firefox moved to multi-process before moving to WebExtensions.
And? Removal of XUL addons were still a prerequisite for the multi-process architecture. Mozilla just realized that WebExtensions was a sane, performant extension API that worked well with e10s, and would useful for compatibility with Chrome.
> You've lost count of how many mass extinctions the Firefox extension has been through
Two? Hardly a lot.
The XUL model is inferior to the Web Extensions model. No amount of trying to cherry-pick specific instances of extensions that had local functionality or performance losses will detract from the facts that (1) the XUL addon system was inferior and (2) had to be removed in order to make Firefox (both the browser and ecosystem as a whole) more performant, secure, stable, and easier to maintain.
