User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.7; rv:11.0a1) Gecko/20111207 Firefox/11.0a1 Build ID: 20111207031110 Steps to reproduce: 1) Load a complex page, such as engadget or Facebook. 2) Using a trackpad (laptop or magic trackpad), scroll down on the page with a flick. Actual results: Scrolling in chrome is fast and smooth. Scrolling in Firefox is slow and choppy. Sometimes, the page appears to jump a bit when scrolling. Expected results: Scrolling in Firefox should be fast and smooth.

What are your settings under "Advanced > General > Browsing > Use smooth scrolling / Use hardware acceleration"?

Hardware acceleration is enabled. Note: this is an 8 core Mac Pro (mid 2009 model) with an ATI HD4870 and 12 GB RAM.

This is almost certainly true, but there's not a lot to go on here. :/ Michael, do you know how to use Shark or Instruments to profile?

Alas, I don't.

But don't you have this happen as well? It happens on all of my machines - even my fastest ones.