[thrdbndndn]

When the transition from XPCOM to WebExt started, Mozilla made some big promises about the functionality parity about the two but failed to deliver most of them (and silently removed such promises from their official pages, and left relevant Bugzilla tickets rot (e.g. https://bugzilla.mozilla.org/show_bug.cgi?id=1427928 )).

IMHO, practically speaking, the final result of WebExt isn't that bad, especially taking into consideration of the added APIs you mentioned.

It is the shear difference bwtween promise and reality that really hurts lots of power users and addon developers to this day.

Also you mentioned Treestyle as "most of the popular ones", but left out the elephant in the room, Tab Mix Plus, which even has its own Bugzilla ticket: https://bugzilla.mozilla.org/show_bug.cgi?id=1226546 Gesture extensions nowadays are also pretty limited compared to its heyday due to the nature of WebExt.

In hindsight, these promises were just too good to be true, but people were believing.

And the story of extension support on Firefox on Android is way too similar to the last time in the Fennec to Fenix transition. At least this time, users just didn't have much faith in it to begin with.