Whenever Firefox comes out with a new version I try to use it for a week and realize it just doesn't perform as well as Chrome. Theres always one or two sites like twitch where it just LAGS to death whereas in Chrome its smooth as butter. At this point I just go back to it. Sigh...
Are you using mostly Google pages or services? That might explain why Firefox runs worse. Anecdotally, of the three browsers I have on my dev machine Chrome is the biggest resource hog.
The reason Chrome doesn't lag is probably due to the fact that it uses so much RAM. I personally use Safari because of the OS integration but for some sites I do have to fire up Chrome just for performance.