I switched from Firefox to Pale Moon, you may want to look at it. It's an optimized version of Firefox. It has a lighter memory footprint and seems faster.
It has some developers tools missing by design but 99+% of people will never miss 'em. There is a software migration tool to copy your setup and options from Firefox but I didn't use it. I just started from scratch. Haven't found any add-ons that don't work.... yet...
OH, and just typing those letters and implying that browser from WinBlows is bad for your memory... ;-)