Hi I have had a look into this and have a couple of solutions for you. If you mainly look at YouTube videos when you are online, you may not need the Flash plugin that you have installed. Firefox has the built in ability to play YouTube videos without Flash. You can read how to uninstall Flash [https://helpx.adobe.com/flash-player/kb/uninstall-flash-player-windows.html here]. If you need Flash for other sites, I recommend having a read of this [https://support.mozilla.org/en-US/kb/keep-flash-up-to-date-and-troubleshoot-problems guide] that will walk you through how to fix common Flash issues. I hope this helps, but if not, please come back here and we can look into a different solution for you.