If other softwares runs fast and smooth it's obvious that it's a Firefox-problem. Probably because of a corrupt profile. I have done a "checklist" you could follow here: https://support.mozilla.com/en-US/questions/667207#answer-124643 Regarding slow start up, it's a common and old problem. Not all FF-users experience it as a problem, but I used to belong to them who suffered. If your cold start up (the first start after a Windows boot) is really slow, but a warm start (the second time you restart Firefox) is much faster - then I think I can help you. Try my own simple solution here: https://support.mozilla.com/en-US/questions/762446#answer-119951 I run on Win 7 64-bit and on Firefox 4.0 betas, but that doesn't matter as it works also on older Windows and Firefox versions. Regarding your anti-virus software. I have tried the most of them. The best tradeoff is in my opinion Eset Smart Security (NOD32). If you want to try it: http://www.eset.com/download/free-trial/international I hope this will help you :)