I have some similar issues. Sometimes Firefox lags after loading the page (around 1 sec), but eventually works fluently afterwards. It feels like it needs to warm up the engine.
I noticed that disabling "smooth scrolling" in the settings helps with initial scrolling issues.
However, in general I have the feeling that FF57 is faster than before. Could also be that I now focus on the loading times more than usual. A restart of Firefox helped yesterday after the upgrade to 57.
I have a MacBook Pro 2015 and am Firefox user since 1.0 ;-)
I noticed that disabling "smooth scrolling" in the settings helps with initial scrolling issues.
However, in general I have the feeling that FF57 is faster than before. Could also be that I now focus on the loading times more than usual. A restart of Firefox helped yesterday after the upgrade to 57.
I have a MacBook Pro 2015 and am Firefox user since 1.0 ;-)