I'd do a scan for any malware, bots etc, just in case; maybe time for a defrag too? What OS are you? Although I love Firefox I find it more memory intensive than IE on the whole, and blows up more often, but then I suppose I have more extensions than most, some of which, like firebug, get under the covers somewhat. I've found Google Chrome the quickest and lightest so far, but it's still in Beta form.