Symptom for me is usually the phone actually starts vibrating before doing anything else. Screen tries to rotate to portrait but takes ages to do so and is unresponsive when it actually does. In some cases it can go to voicemail before I even get a chance to answer.

I still use adblock, despite the known memory leaks, which I believe to be the cause for me. I can't stand the sight of all the ads and it helps reduce data usage. IIRC I'm using a slightly newer version for FF3.6 (1.3.10 vs 1.1.1 on garage site) that I modified to accept microb being based on the beta but it still leaks like mad. I did manage to get the latest version installed a couple of months ago in Microbe but couldn't get the interface for adding subscriptions to work.