I have the same issue on debian lenny 64bits with firefox (iceweasel) 3.0.4-1.
I also use the flashblock extension, but with the last version 1.5.7.1, and I have the issue...
So lessoffensive, flashblock version 1.5.7.1 does not solve the issue in every case. (I also use nvidia drivers from nvidia.com)
I tried without flashplugin-nonfree and without flashblock, but it crashes again.
I have the same issue on debian lenny 64bits with firefox (iceweasel) 3.0.4-1.
I also use the flashblock extension, but with the last version 1.5.7.1, and I have the issue...
So lessoffensive, flashblock version 1.5.7.1 does not solve the issue in every case. (I also use nvidia drivers from nvidia.com)
I tried without flashplugin-nonfree and without flashblock, but it crashes again.