See: * https://support.mozilla.com/kb/Firefox+launches+automatically+when+your+computer+starts --- * http://www.apple.com/findouthow/mac/#tutorial=startup - Open Applications Automatically on Startup * Control-click on its Dock icon and uncheck 'Open at Login' * Click Accounts (in the System row of the System Preferences window) ** Click the Login Items tab ** Click on Firefox in the list ** Click the Minus (-) button