Vista Issue of the Day - Firefox 2.0 CPU Utilization

OK, this isn't really a problem with Vista per-se. But I've noticed that when running Firefox 2.0 on Vista, it's constantly spinning the CPU at 15-25%. Restarting Firefox doesn't seem to help, I have just a few tabs open, and they aren't doing much of anything, And yet the CPU utilization for the process is constantly between 15-25%. I certainly didn't have the problem on XP. Is anyone else seeing this?

UPDATE - It looks like the Mouseless Browsing extension was the cause of this. After disabling it, CPU utilization of Firefox drops to negligible when idle. Either a) this was a problem on XP and I never noticed it, or b) the extension does something which causes the CPU problem on Vista but not XP. More research required here. Too bad, I dig that extension.