Firefox isn't an acceptable alternative, over the past few years it's completely obvious the priorities of the organization in control of it are not to build a great browser and to de-homogenize the web tech stack.
Best thing that could ever happen for the browser problem is for Mozilla to go under and FF be taken over by the community who actually care about the problem that FF is the solution for, not just some overpaid executives who think selling a VPN is a good use of their time between private jet flights.
I use Firefox as my daily driver and I couldn't disagree more. But it's hard to reply adequately because you don't actually tell us what your problems with it is. In what ways is Firefox not an acceptable alternative?
The parent comment seems to be referring to some of the things Mozilla has been doing lately. I'll focus only on the browser.
I think it's fair to say that the experience with Firefox will depend a lot on the platform and how much its imperfections affect you.
For example, I use macOS. Until last year Firefox would cut my laptop's battery life in half compared to a Chromium browser. That alone would make it a bad browser for me. Some sites that rely a lot on JS are often noticeably slower than Safari or Chromium. Then you have Firefox's UI. One thing that annoys me... CTRL/CMD+Click means opening on a new tab, right? On Firefox, by default, links on pages works like that, but links on the bookmarks bar don't! Talking of the bookmarks bar, after many UI updates, it no longer has the correct margins and doesn't fit with the rest of the UI, not to mention that favicons are a pain in the rear to update. And then there are the little things... Firefox moved to a "settings in a tab" for some things, but stuff like downloads and the bookmarks manager still open on windows with sizes that don't fit the OS or even Firefox's design. This old code was also stopping context menus and other parts of the browser from using the OS dark theme until recently.
Is Firefox terrible? No, but it's a mix of old and new code, UIs, etc, and the macOS version has been neglected for years. It's usable. Firefox's problem on this platform is that Safari and Chromium are so much better platform. Even with the recent improvements, Firefox is still behind in many areas.
I use Firefox daily, but only as a secondary browser. I've tried... but I get annoyed after a week or two and end up going back to a Chromium-based browser.
My problem is with the organization, their mismanagement has already cost it a huge amount of usage % and it's only going to get worse because it isn't their priority.
An alternative isn't an alternative if no one uses it therefore no one tests or supports it.
Best thing that could ever happen for the browser problem is for Mozilla to go under and FF be taken over by the community who actually care about the problem that FF is the solution for, not just some overpaid executives who think selling a VPN is a good use of their time between private jet flights.