scrolling up-down in Gmail is so choppy and slow in Linux (Ubuntu?) with Firefox. Looks like this is because of excessive use of Javascript in Gmail. The only alternative that I know is changing the Gmail to Older Version, you can do that so by clicking on the <link> (you can also find this link in your Gmail, at the very bottom line, you’ll find the link to Older Version). I know this is some crappy Idea!

But, I hope that this helps!