Just like a lot of people are still using the insecure Windows XP, a lot of Firefox users are still clinging onto old versions of Mozilla's browser. The foundation hopes to change this by pushing people to upgrade their browser. For Firefox version 11 and higher the company will use the browser's integrated hotfix feature to download the latest version of Firefox in the background. The user will then be prompted with a screen asking to install the latest version of Firefox. For versions 3.6 and earlier the major update will be served as if it's a minor update so that things like add-on compatibility checks are avoided.
Smedberg mentioned that user preference will be respected, so "if the user has updates completely disabled in preferences, [Firefox] will not prompt for updates at all." He continued on to detail that if the manual updates option is selected in a user's preferences, then Firefox "will nag but not force-install the update."
Firefox versions 11-26 will be targeted in a slightly different way-- an add-on with a hotfix for bug 994882 will be distributed instead. Two methods of deploying the update are currently being considered: the first involves silently downloading the update, and then prompting users with a UAC dialogue on the next launch. If the user clicks "yes." which most would automatically do, then the latest version of Firefox will open instead of the older one they were expecting. If the user clicks "no," the old Firefox will open as normal, however a tab will open asking if the user wants to use the new Firefox. Refusing it is not permanent, and the user will continue to be nagged to use the latest version of Firefox