The number of tabs I have concurrently varies, but I suffer from this problem as well. It may also be a dodgy extension.
FWIW, I've the following extensions:
- ....... Plus
- British English Dictionary
- Forecastfox
- FoxClocks
- GMail Manager
- Google Toolbar
- Talkback
I also have iFox theme in use.
Everything is up-to-date.
At its worst, it got up to 99% CPU utilisation and about 90Mb memory usage.
I don't recall this problem when FF2 was first released. Since updating to 2.0.0.1, this problem occurs more often.