Some times firefox really lag or hang. I tried resetting and disabling most plugins (actually only Java and Flash enabled). It happens that not only "it lags" but it slow down the whole system, so the operative system is slowed so down that it can't actually detect Firefox as "not responding" for closing it(theorically using a dual core and since applications are time-sliced the operative system should not be slowed down.. not so much at least) The only way I had a similiar effect when was I wrote a small virus to test on my machine only (It was just allocating a 100MB array and then accessing random array locations). The problem may be excessive memory moving/copying with firefox, that could (as my harmless virus was doing) slow down the system to that level because a whole cache page is loaded every 2/3 cycles of clock. Hope you can somewhat profile that. cheers.