I spent last days free time to test two browsers: Qupzilla and Pale Moon,
which should be lightweight but powerful at the same time.
Qupzilla: very fast, responsive and load almost all sites perfectly, but
crashes when the CPU is under heavy pressure (e.g., when loading lot of tabs
simultaneously)
Pale Moon: as above, but this one never crashes! I tried to open 35
instances* of heavy sites (Facebook, Youtube, Gmail) and it has never freezed
or crashed!
*: I enabled uBlock Origin and QuickJS as onpon4 suggested me.
I think I'll stick to this one!