I have just noticed that the Javascript scrolling gig list causes high CPU on my system on the latest Firefox 3.6.3 (on Windows XP SP3).
With only Firefox running, and with one tab open at the Manband Forum, Firefox uses about 25% CPU on my dual processor system (i.e. about half a processor). If I open up a second tab with the Manband Forum, it maxes out at 50% CPU (i.e. 100% of a processor).
I can reproduce this behaviour on another system. Also, IE & Chrome do not exhibit the problem.
If I disable Javascript, then the CPU problem goes away. In fact, if I hover over the scrolling gig list with my mouse cursor, then the gig list stops scrolling and the Firefox CPU usage drops to zero (ish).
Looking at the Javascript, it uses "Cross browser Marquee II" for the scrolling gig list. Googling shows that this is a known problem (which has actually been around for at least a year), with a suggested fix to initializemarquee():
http://www.dynamicdrive.com/forums/archive/index.php/t-41987.html