[antisthenes]

It was usable as a main browser at some point between 4.0 and the current quantum (read - when 90% of the useful extensions were axed and the only advantage over chrome was thrown out)

I can't tell whether it's mostly web 2.1's fault or Firefox's gross mismanagement and stubbornness

[jamesgeck0]

Firefox still has an edge over Chrome here; Mozilla continues to add new Web Extension APIs for frequently-requested functionality. For example, this release added tab hiding, making it possible to build extensions that add Panorama tab groups.

Anyway, maintaining the old extension API wasn't sustainable. Many older extensions broke repeatedly due to refactoring efforts like Electrolysis. These refactors ultimately resulted in some of Firefox's current speed gains.