in debian based linuxs the security fixes are put into the existing version of softare so the fixes in the official firefox 10.0.3 and 1.0.4 get 'backported' to the ubuntu 1.0.2, and released as 1.0.2-ubuntu1, 1.0.2-ubuntu2, etc see http://ubuntuforums.org/showthread.php?t=33475