"With Flash Player 18, in the vast majority of cases, the installer will no longer display a dialog to shut down the currently running browsers or applications that are using Flash Player!
Once the installation is completed, you will be notified that the browser may need to be restarted to use the newly installed version. This requirement depends on your browser’s ability to see the new version. Either way, Flash will continue to work and you can easily force the new version to appear by simply restarting your browser when it’s convenient for you."