If you are using Firefox 3.6.'''6''' or above, a new preference was added to the Connection Settings proxy preferences in Tools > Options > Advanced >> Network tab - Connection = Settings = '''Use system proxy settings''' The default setting is for '''Use system proxy settings''', ''which can prevent LAN connections from being made, like you experienced. AFAIK, it can affect almost any local network device that you interface with using a local IP address, like routers, NAS devices, and such.'' If you select '''''No proxy''''' and restart Firefox your problem should be fixed.