Hiya!
I'm not sure what causes these problems but i did a clean install for my pc last night and everything was very good, but after i ran CCleaner only one time to do the cleaning my modem went crazy and started to loose internet connection repeatedly, it makes my modem to search internet connection all the time and i can only approx search web 5 minutes then it starts to search internet connection, before my lag was 38-45ms but after i used CCleaner it jumped to 23kms.....i mean wtf is this!! I had to wipe my hd clean and reset my modem to factory settings to get my modem work again and not showing 23kms lag anymore, then my Firefox started to work normally again..
I have Windows 7 x64 SP1 & Firefox Nightly 10.0a1
When i did a clean install second time and did not use CCleaner everything is OK again...