I virtually never comment on Ars, but I feel very strongly about this subject. I used Netscape Navigator (and Mosaic before it), switched to Mozilla when it first came out, and switched to Firefox when it came out. I've used it ever since.
But Mozilla has an absolutely massive footgun, and they appear determined to keep using it.
Every few releases, they do one or more of the following:
1) Add new anti-features that I don't want, and which they go out of their way to hide the way to disable them. A lot of them have no UI setting to control them and need to be disabled in about:config. They're features I don't want, will never use, and which have questionable impacts on privacy.
2) Remove controls and settings which I use for better privacy. Sometimes they live on in about:config, but sometimes they're just gone.
3) Outright remove features I use. Sometimes someone has reimplemented them as an extension, but sometimes that's just not possible due to the limitations of the non-XUL extension framework after they dropped XUL.
4) Make gratuitous changes to the UI which actively harm usability. I'm not talking about things that just require a period of adjustment; I mean things that no matter how long you use them, it is more difficult to actually use the browser for browsing. Sometimes they leave a setting there for you to switch back, but not often, and those settings usually go away in the next release or two. You have to go hunting for someone to have figured out how to reverse the breakage using userChrome -- and note they've disabled the ability to even use userChrome by default -- you have to enable it in about:config. Some of these UI changes simply cannot be worked around, because of the limitations of extensions and userChrome.
Perhaps worst is that if you try to report these types of issues with usability or deleted preferences, their response isn't "How is this change impacting your usage of Firefox?" or "What problem is this causing?" or even "Unfortunately it's no longer possible because of <required change> which we introduced for security reasons". It's usually "You shouldn't want to do that." Completely paternalistic, and absolutely unwilling to see that not all users have precisely the same needs and requirements in using a browser.
I still use Firefox. But I no longer recommend it to anyone else. And I can see the day coming when I will switch to a non-Chrome Blink-based browser like Brave or DuckDuckGo's which still believes in user choice and privacy. Unless Mozilla make a serious change in their approach to Firefox and their users, they're heading towards 0% market share.
C.
