brotherhood_of_LAN - 9:01 am on Jan 10, 2013 (gmt 0)
Under "known issues" it has "For some users, scrolling in the main GMail window will be slower than usual (see 579260)"
I've noticed sometimes on YouTube too that videos won't load up the first time round, second time round... in what appears to be a random thing. Sometimes it works first time, sometimes not. The paranoid in me says that they do this on purpose alongside a "try chrome!" ad.
I still use FF out of habit, it "works" but Ive found Chrome to be faster.