User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:41.0) Gecko/20100101 Firefox/41.0 Build ID: 20151014143721 Steps to reproduce: Download and install Firefox 42.0. Three out of the four times, Firefox did not re-load after installation, so I re-booted successfully. Later, I got the typical pop-up telling me to install Firefox 42.0. Repeat. This has happened with previous updates, too. Desktop computer running Windows 7. Actual results: Keep getting pop-up telling me to install the new update that I already installed. Expected results: Firefox 42.0 should have installed, and the alerts to install it should have stopped.
Did you try to create a new profile (see https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles) and update Firefox to the latest version from this new profile?