I migrated to Pale Moon from Firefox
and everything just worked. All my FF history files, passwords, even cookies ported over from Firefox as simple file copies. Amazing.
Pale moon doesn't abuse you if you want to accept self-signed certificates, and it doesn't have Australis stuff, and it doesn't freeze every few accesses to Google sites. Also, their ATOM based version works really well on the old XP netbooks the family still uses...
The only important plugin which didn't work is FireFTP, so I keep an old copy (v29) of FireFox around, as the new FF don't work properly with that plugin, either...
Thanks to the developers who enable all this flexibility...