engine - 5:50 pm on Mar 12, 2010 (gmt 0)

https://developer.mozilla.org/devnews/index.php/2010/03/11/upgrade-offer-to-be-issued-to-firefox-3-and-firefox-3-5-users/

Starting today, users running older versions of Firefox will be offered the choice of upgrading to Firefox 3.6. We’re presenting this upgrade offer for our users who may not realize that a new version is available

The offer screen will only appear after 60 seconds of keyboard inactivity to ensure we don’t get in the way of anyone’s activities. If a user declines the offer and later regrets that choice, they’ll be able to get it again simply by selecting “Check for Updates” from the “Help” menu.