The update will appear as a minor update so any user with auto-update enabled will see the new version downloaded ready for installation when the browser is restarted. The current plan aims to see Firefox 3.5 out of widespread use by the end of June by offering Firefox 3.6.18 to both Firefox 3.6.17 and 3.5.19 users on 21 June, the same day as Firefox 5 is to be released. Ideally, Mozilla would like to upgrade them to Firefox 4 or the forthcoming Firefox 5, but would be happy with them moving to the latest Firefox 3.6. According to Mozilla there are approximately 12 million people still using Firefox 3.5, despite numerous prompts through the default Firefox/Google search page, whatsnew and firstrun prompts and other broad hints to upgrade.
Mozilla has created a plan to aggressively end the life of Firefox 3.5 by using auto-update.
