Firefox 3.5.3 introduced a new feature which would check the Adobe Flash Plugin upon first restart after installing the update. Mozilla is working on getting a ‘Plug-in Check’ page launched later this month that users can visit to check their plug-ins status. Further Firefox 3.6 will be able to check and notify the user of new updates for their plug-ins, just like Firefox currently does for extensions and themes.
Source: Mozilla Links
The Firefox Extension Guru's Blog 