Security Issue, please update your Flash 21.0 r0 by removing it with this tool : https://helpx.adobe.com/flash-player/kb/uninstall-flash-player-mac-os.html Reinstall with Flash Player Version: 30.0.0.134 Current Version https://get.adobe.com/flashplayer/otherversions/ Step 1: Select Operating System Step 2: Select A Version (Firefox, . . . .) Note: Other software is offered in the download. <Windows Only> As we do not know what you are listening to HTML5 or Flash please do the above. *https://support.google.com/youtube/topic/3014746 *https://support.mozilla.org/en-US/kb/fix-common-audio-and-video-issues *https://support.mozilla.org/en-US/kb/html5-audio-and-video-firefox We do not know your security software, what is it please ? Nor what Extensions ou are using : '''Try Firefox Safe Mode''' to '''TEST''' & see if the problem goes away. [[Troubleshoot Firefox issues using Safe Mode|Firefox Safe Mode]] is a troubleshooting mode that temporarily turns off hardware acceleration, resets some settings, and disables add-ons (extensions and themes). '''If Firefox is open,''' you can restart in Firefox Safe Mode from the Help menu: * Click the menu button [[Image:New Fx Menu]], click Help [[Image:Help-29]] and select ''Restart with Add-ons Disabled''. '''If Firefox is not running,''' you can start Firefox in Safe Mode as follows: * On Windows: Hold the '''Shift''' key when you open the Firefox desktop or Start menu shortcut. * On Mac: Hold the '''option''' key while starting Firefox. * On Linux: Quit Firefox, go to your Terminal and run ''firefox -safe-mode'' <br>(you may need to specify the Firefox installation path e.g. /usr/lib/firefox) When the Firefox Safe Mode window appears, select "Start in Safe Mode". ;[[Image:SafeMode-Fx35]] '''''If the issue is not present in Firefox Safe Mode''''', your problem is probably caused by an extension, theme, or hardware acceleration. Please follow the steps in the [[Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems]] article to find the cause. ''To exit Firefox Safe Mode, just close Firefox and wait a few seconds before opening Firefox for normal use again.'' When you figure out what's causing your issues, please let us know. It might help others with the same problem.

This can happen if you have a multi-channel sound system that doesn't report all channels properly. You can set this pref to true on the <b>about:config</b> page to see if that works. *media.forcestereo.enabled = true You can open the <b>about:config</b> page via the location/address bar. You can accept the warning and click "I accept the risk!" to continue. *http://kb.mozillazine.org/about:config