In a page with many animated gifs. The gif animation is very slow and in Linux (Redhat 6.2, Sawmill WM and XFree86 3.3.6) the mouse movement gets very laggy and the pointer jumps as you move it. This is related to Bug 44588 but adds mouse performance problems.
I suspect that this is partly an artifact of what video card someone has (and how well your X server supports it). My system shows no perceptible lag, although X plus Mozilla are soaking up almost all of the CPU to do this. With a video card that is not well supported, XFree86 might well be spending a lot of (unresponsive) time shoving pixels around. For comparison purposes: RH 6.2, XFree86 4.0.1, Matrox G400 MAX (32MB) at 1280x1024 24-bit colour. (And a lot of memory and CPU.)
Yeah, that pegs my PIII 450. I'm confirming this, since it is a pretty unacceptable performance issue. I think it is a dup, though I can't find it.
Dupe is of bug 44588, if someone can mark it as such. I don't seem to be able to.
*** This bug has been marked as a duplicate of 44588 ***