I have had such instability issues with Firefox lately that I have temporarily switched to Safari. I started noticing this on 1.5, but has only gotten worse on 3.5, including 3.5.2. Here is a list of observations: 1. On my Mac, if Firefox is idle for a good time, say a number of hours, it tends to become very sluggish, sometimes even locking up. 2. I used to sleep my system overnight, and 90% of the mornings, Firefox would be locked up. 3. About 50% of the time after sleeping the system overnight, my whole system would be locked up. If not locked up, then the whole system would be very sluggish until I force quit Firefox. 4. I temporarily solved all of these "sleep-overnight" issues by making sure Firefox was shut down before sleeping the system. After doing this, the system just wakes up immediately and works well, like it did some time ago, before the Firefox issues. 5. My son using Vista is reporting the same set of things, in that Firefox locks up itself, and it locks up his whole system, requiring a system reboot. So similar, but worse (yeah, Windows, I know). In any case, it seems there is a problem with Firefox. So I started using Safari in the meantime. Anybody else seeing such?