how to temporarily disable mozilla

Mozilla Firefox doesn't block other programs from being installed, unless those programs need Firefox to be closed so they can update Firefox (e.g., Flash player). Anyway, to stop Firefox from running, simply exit all windows of the program (File > Exit). '''Added thought:''' Any program that makes you take down all your security defenses in order to install is automatically suspect in my mind. Are you sure the program you want to install is genuine and not some kind of malware? You might want to run a few extra scans on it (for example, upload to virustotal.com).