Well, I'm on the latest Firefox. It's rock stable. Sure it's heavily bloated as I said before, and eats RAM like crazy. I have tons of open tabs, and it sure uses several GB and 14 processes. Not very optimal, but it's still the browser that works best for my needs. It's 100% usable. Now of course on a small machine with low RAM, I might look elsewhere. Not bothered on my main workstation which has 64GB, and not either on my laptop which has 16GB.
For privacy reasons, I wouldn't touch Chrome with a stick, so I'm OK with Firefox. I've tried alternatives occasionally, but they rarely come close (again for my needs), so I've never switched so far.