I haven't looked at your code but I encountered a similar problem on a site I was building, the scrolling was fast in every browser except firefox. Turned out that firefox doesn't dispatch scroll events as quickly as the others, but I found a function which fixed the problem:
http://blog.keithclark.co.uk/faster-scrolling-parallax-websi...
Might be irrelevant but I thought I'd drop this in, in case it was useful.
Re:Ask HN: Feedback on startup, Fol.io
by cilliankieran on Monday June 18, 2012 @07:16PM
(#4129086)
Thanks James - will certainly take a look. I'm not sure if this is related or if it's simply the number of assets being loading are struggling on different browsers.
Cheers.
Cheers!