I think forks, such as Librewolf or Waterfox, will live for a while even if (and that’s a big if IMO) Mozilla comes down. Consider donating to them (and to Ladybird).
Vouching for librewolf. Not only does it not bother me with things like pocket and "Firefox sync", it also does not track me, and the browsing experience is genuinely superior.
I didn't realize how much webgl and other cruft slowed things down until I started using librewolf.
The one improvement I'm hoping for is that the project would be checked into the official Debian/Ubuntu/Fedora package repos as those are less risky than the repo controlled by the developers.
Is it possible to do things like "send tab to device" using Librewolf? Sometimes I'll stumble upon a programming library in my feed on my phone and I want to send it to my desktop, and Firefox sync makes that possible.
Yea, I use Firefox sync since I'm still using Firefox, but with the way things are going I'm looking for a ship to jump to that still supports my workflows.