Ok a little bit ago I went over to my friends house who is using Windows Vista, and they wanted firefox on there computer. So I downloaded it on there and everything worked fine. Later that night the internet went out completely. Now I work for Comcast HSI so I figured this wouldn't be dificult at all. I powercycled the modem, checked for proxies, made sure the tcpip was obtained automatically, release/renewed the ip. After all this, still wasn't working. So I turned of the computer completely for about 1 minute or two unplugged the modem then plugged it back in before rebooting the computer, and it worked, but only briefly. I was surfing fine, then I closed the browser and reopened it and it was back to where I started. I'm kind of clueless with this windows vista and I personally think it's a piss-poor OS. So anyways, if anyone has any tips I'd greatly appreciate it.
i tried Firefox on my vista machine too and was having problems, so I installed Opera which is identical to firefox, more secure and many add ons too. That is what I use now, and haven't had a problem. I love the tabbed browsing that firefox let you do, then I found out Opera did it so bam, i am a convert.
Try removing the NIC from the Device Manager..right click it, and uninstall it. Restart the computer.