I actually use CCleaner as well. I'll try explaining my problem a little bit better see if you guys can help me out.
I have two computers a Macbook (connected wirelessly) & Desktop (direct connect). I use Firefox on my Desktop, its set to delete/clear browsing history on exit. I've been using Firefox for quite a few years now and never had no problems. So I did a clean install on Windows 7 & have been noticing this problem ever since.
Let's say I go to a certain website on my Desktop, it keeps saying ''page unavailable'' or doesn't load. Now, when I go on my Macbook and try to go on the same website, it works. Only difference is, I tried going on the website while connected to a public WiFi instead of my own. Now when I connect on my Macbook to my network, I get the same problem as my desktop, doesn't load. I'm not sure if this a browser problem or a problem with my router. I'm using Linksys WRT110 (if that helps). Sometimes when I connect to my network, the website will load no problem, but not on the desktop. I can even access the websites on my Blackberry....
I'm not sure if my browser/router or w/e isn't picking up on the domain IP's properly, or its blocking something out....