Do you have any similar issues with other programs? If so, a format C:\ is probably the easiest solution.
You mentioned your HDD only had 40GB free, you might consider running a defragment or two, as well as a disk check (
Don't bother with the Windows one).
Did you change anything else around the same time you installed v2.0.0.9? If so, revert it and see if the problem goes away.
FF 2.0.0.14 is out. Who knows, maybe your problem is a known bug that's been fixed in this version.
If all this fails, open the task manager and see what your processor is doing when you open a page. Memory usage might also be interesting.