I run W7 SP1 with Thunderbird 7 and Firefox 7. Quite often after clicking a link in T'bird to open F'fox, the PC will become very very slow or even stuck. When it becomes slow there's a lot of HDD activity but it's so slow that opening the Task Manager is not possible. Anyone got any ideas as to what's wrong or how to trace the problem? AVG Internet Security & Windows Defender find nothing untoward.