You must '''properly close''' Firefox with Exit not with Close Window. # Alt+F, X ( File > Exit) -- the "X" in upper right corner merely closes the Window, don't count on it to close Firefox # Verify Firefox is actually closed through the Windows Task Manager: Ctrl+Alt+Del, then choose Start Task Manager then make sure you are looking at the '''Processes''' tab, if you see firefox.exe the close it by right click on the row, then end process tree Looking at the Application tab instead of the the Processes Tab will not help you, you need to look at the Processes tab. If the installation asks you if you want it to start Firefox for you refuse that, after the installation finishes., start Firefox in the normal manner, that way way you avoid the possibility of creating another profile and can creating confusion by invoking the wrong profile.