I've been using "Firefox" since it was Netscape:
* partially of of habit (why change if it works),
* a load of trust in Open Source and they weren't out for "my data"
* I used Mozilla as a "trust anchor" for my On-Line presence including Emails (Thunderbird) with contacts & calendering (started off as an external plug-in)
I stopped using Mozilla Thunderbird when all the plug-ins (including the virus scanners) and Cardav|Caldav integrations broke (now Evolution)
I stopped using Firefox on Android when they totally messed up the UI, the military term of FUBAR springs to mind! (now Vivaldi)
I still use Firefox on the desktop, although the "Great Plugin Purge" removed a load of "none backward compatible" and now broken integrations.
I think the only thing stopping a complete collapse of what used to be an amazingly innovative collaboration/company is the almost "compulsory support for a competitive technology" by Google, with them covering their asses saying "Look, there is a free alternative", whereby they have long dictated what a web browser must do to survive. There really is little choice now but "Chromium based" solutions.
Sorry for the rant, but I am sad to say it, I think that it won't be long before I'm installing Brave, or something like it on my PC too, because Mozilla ceased to exist.