I recently installed ubuntu 11.10 and had no issues co-existing between the firefox versions, once in a while booting back into windows and vice versa. More recently, after an update in ubuntu, I rebooted into Windows 7 (64) and launched firefox, and when I did my network would lose connectivity to the point of not even being able to hit the gateway. The only way to restore would be to reboot or run a netsh restart command. I ended up restoring default conditions to windows firefox by starting in safe mode this morning and the issue at the moment no longer occurs.