Maybe see what memory usage is like in a new Firefox profile. That'll be essentially like a factory-reset Firefox, but you can always switch back to your old profile, if it does not change anything.

Type "about:profiles" into the URL-bar and from there it should be mostly self-explanatory.

I wiped out Firefox and observed this memory hungriness with a completely clean install with no add-ons whatsoever versus a Fully configured Chrome.