As long as they can't manage to make a half-decent mobile browser this hardly matters.
Performance improvements are nice and all, but unless the performance is truely terrible, it's the least relevant factor.
Much more importent are:
- consistently good UX over all platforms, together with good sync
- good support for all websites
Their Android version is completely useless since the reboot (which is especially sad since the version before was hands down the best UX for a mobile browser on the market). They even dropped their VR version, even though it was literally just their Android version with slightly adjusted UX. They don't even have any form of tablet UI or Android TV UI.
And since their market share is steadily approaching zero, more and more websites drop support for FF and it's noticable.
The support part is what really kills FF, since it's not really in their hands whether web devs test websites with FF.
Lower market share -> less support -> lower market share.
Especially users who "just want the browser to work" are affected by that. They don't care much about the browser, but about the websites. And if their favourite websites tell them to stop using FF, they will. And that kind of user makes up the biggest part of the market share.
And since FF has no platform where they can push their browser (contrary to all other major browsers), they also won't get new users.
As much as we would want it otherwise, FF is dead, they just haven't accepted it yet. And that's true for almost all Mozilla products and Mozilla itself.
The only way I see how this can be reversed is if e.g. the EU decides that Mozilla and/or its products have some special value and starts funding and pushing them.