I installed NIS2009 and started having this issue with Firefox 3.05.
So, I upgraded to FireFox 3.0.7 with the same results. I suspect that
NIS2009 has something to do with this, but many people say it does
not. My wife's system works fine with FireFox and NIS2009. Usually it
pops up the Crash Reporter on shutdown, but ...rarely...even while on
a site.

So, before I start disabling add-ons/extensions, can anyone tell me of
any known conflicts so I may be able to disable a likely "culprit"?

I have read some of the posts about this but they all seem to say it
can be anything.