In the end, they lost both the power users and the regular crowd (which will use Chrome or Edge, because those come bundled or are advertised on front page of Google).
And, of course, "being user-friendly to normies" has always been among Firefox's chief goals.
Then I finally switched to Chrome because it was much faster than FF and my extensions were dead anyway. I switched back a few years ago because FF became good enough again. I wouldn't be surprised if others did the same (and possibly didn't switch back).
When I switched, everyone I provided tech support in my family for also switched. I did not switch them back because I don't think it's worth inconveniencing them at this point.
Obviously my case is a miniscule amount of people, but it wouldn't surprise me if the story wasn't somewhat common.