The quick fix for this problem, at least for my own sake, is to increase the time between each of the saves performed by session restore. By opening about:config in your Firefox address bar, then typing browser.sessionstore.interval in the filter box, you'll see a value of 10000, which is in milliseconds. (Meaning your session is saved every 10 seconds.) I changed this to 300000, or every 5 minutes, as I don't have the urgent need for tab restoration. If you feel like being more on the safe side, try increasing it to something a bit lower, say 120000, or every 2 minutes.

Thanks for your input. I have seen this suggested elsewhere and tried it before. Unfortunately, it hasn't resolved the problem. I've left the setting at 300000. Anyone got any ideas? This must be happening to lots of people and it makes Firefox unusable in these circumstances. i find it hard to believe that their tech guys haven't posted a proper fix all over the net! Here's hoping.