Firefox is great, maybe its more secure than IE (I dunno tbh) but as I had no problems with IE and need it for work, and its on every machine anyway, I went back to IE. I use Safari (Apple) sometimes when I need to check something out in a different browser.
Well I did have problems since - plenty of them and if anything it got worse.
Flash of inspiration - ran Firefox in safe mode, disabled everying non-essential (including the AVG toolbar which I have a strong suspicion may have been part if not all of my problem) and everything 100% for the last 3 days.