Firefox is urging people to update to the latest version 1.5.0.2 as some security loopholes has been discoverd. This may also concern Thunderbird and Seamonkey.
More can be found here: http://news.bbc.co.uk/1/hi/technology/4925606.stm
More can be found here: http://news.bbc.co.uk/1/hi/technology/4925606.stm