Firefox has updated older versions to address vulnerabilities related to memory corruption forcing users to disable Javascript. Version 3.6 is already patched and these updates only affect older versions such as 3.5X, 3.01X. Why update older version you say, well many companies update cycles are different and if they have internal web applications which have not been tested on the newer version they are hesitant to perform the upgrade right away. Home users should perform the upgrade right away.
Users should apply the patches, more importantly they should make sure they are running the latest version which can be found here.