Maybe it's an extension or three I'm running but I just want to use the bloody thing not sit there and figure out what extension is not working nicely (and then potentially find out it's none of them) on one platform but is fine on another.
Every so often I go back and have look to see if it's improvised but it hasn't in the last few years for me.
Setting aside the fact that it's as fast as or faster than Chrome, it doesn't crawl any of my machines with >500 tabs (this has 562 as of now).
If you want to dig into your performance numbers there's "about:performance" to see what is using your processor and RAM.
Three year old Mac btw... everything else runs pretty well... if I get a chance I might fire up Firefox in Parallels and see if it's a Mac issue
Give it a go.