Per your '''More Systems Details''' you already have two Adobe Flash Player Plugins. Shockwave Flash 18.0 r0 Shockwave Flash 21.0 r0 An 'invitation' to problems with Flash in Firefox. -------------------- Adobe Flash is notorious for not always removing old Flash Plugin DLL files as part of a Flash program update. Sometimes the user needs to uninstall Flash completely and get a clean start. First, grab the Adobe uninstaller from here: http://helpx.adobe.com/flash-player/kb/uninstall-flash-player-windows.html Then download the latest Flash Plugin version from here: Select the Windows > Plugin-based browsers - the EXE version. https://www.adobe.com/products/flashplayer/distribution3.html Run the Flash uninstaller program, then reboot your PC. Then install the Plugin version of Flash. So you'll have a clean installation of Flash for Firefox.