Well I only have 5, most are for stopping stuff from loading like FlashBlock and Ad Blocker.
I do have a habit of never closing the program down completely, so it just keeps using more resources until it is crawling.
I was using Vista for a long time and had problems with Firefox going RAM-ivore, but since I’ve gone to Win7, I’ve been very happy with FF’s performance. Of course, 12 GB of RAM might be part of the reason.
Here’s a tip - Minimize the FF to the taskbar and then bring it back. The memory allocation gets cut by at least 2/3rds.