WebKit (as used by Safari) was a fork of kHTML (written by the KDE team). And Google forked WebKit. Now we have dozens of Blink forks including Microsoft’s own browser: Blink.

I think it’s pretty safe to assume that forking the code is a low incentive for change

Band-aids like this have existed for many years, plenty of time for Mozilla to listen. And in all that time, they never had the idea to make the band-aids redundant.