On desktop, I've been using Firefox primarily since it isn't Chromium-based and because its releases, ESR and stable, have historically been in the Debian repositories for the time I've used Debian. Compared to the then past usage of Chrome, I liked or became used to the sort of light[er]weight feel to it, and I especially appreciated that it was largely open source and not developed by google.
I tried Brave, but I didn't like it as much, probably more on account of this sort of "feel" of Chromium within it. While the inbuilt adblock/uBO and TOR client were definite positives, I just didn't take to it and I never really used BAT for much even since I didn't really accumulate a lot with it.
I tried Librewolf during the last year (365 days) sometime after I had either realized or seen that Mozilla was going to be going downward in that sense of receding user rights for their software, creeping corporate stagnation, etcetera. I recalled it having most of everything in Firefox, but I initially used the independent, Opensuse hosted apt repository for the packages, which I recall had some server-side issues at some point which preventing me from retrieving updates. It was a blur, but I vaguely recall that I uninstalled Librewolf for that reason and maybe some others and still kept with Firefox.
For a bit, I have been using Firefox Nightly since it had basic JPEG-XL support enabled and I was curious about some features in development for a little bit including potential progress on full JPEG-XL support. Right now, I'm largely being kept on it because it has native tab grouping, and although that tab grouping has a few quirks and bugs right now (I managed to degroup all my tabs tonight

), it is remarkably complete for the most part.
Funnily enough, I was browser touring and hopping just today when I saw this thread. I've been adapting copies of my current nightly profile to a few Gecko browsers/Firefox forks and I had some impressions:
I tried Floorp after seeing [an RSS preview of] the recent LWN article comparing Firefox forks since it was among those named. My initial impression is that I kind of like it as a fork, it has the Lepton theme as a built in option, which I like better than Proton, so cool UI/theming option there. I did realize that Floorp is, however, based upon the Firefox-ESR versions based on a look at the source repository. This is okay, but it does mean the development is going to be behind upstream for a bit, which of course comes into conflict with the JPEG-XL support and the native tab groups I depend upon.
From writing this post, I actually discovered that Librewolf has an extrepo entry in Debian. If it was in the installation instructions page for years, I somehow never recalled that being a method in the first place or its possible I may have disregarded it then; I just installed the extrepo repositories and along with it, Librewolf again. Retrying it again, I don't see many gripes or dealbreakers about it that I can't address in config. Librewolf apparently has the same JPEG-XL support as nightly for the moment, but once Firefox mainlines tab grouping and it makes its way downstream into Librewolf, I will probably be switching to it then.
At some point, I would like to see how Ladybird fares once it becomes tangibly usable, so I'm going to be on the lookout for progress on it when news slips by.