At least once every browsing session I have a page hang with a message similar to 'waiting for www.google.com...'. Reloading this tab will do nothing. I have to click stop, focus on the address bar and hit enter for it to reload. Happened on all version of firefox I've tried on both Windows 7 and Ubuntu. Looking through my D-Link router's logs it showed packets getting dropped when I used firefox. Disabled SPI (Stateful Packet Inspection) on the router and it doesn't happen anymore.
What is the earliest version of Firefox that you know has this problem?