After restarting computer to resolve ongoing very annoying Windows File Explorer issue of not refreshing when renaming, moving, creating, deleting files. NO videos would play in Firefox from You Tube or other sites, only audio with black screen. However, thumbnail images along timeline appear, and full still-frame images display when click on timeline. For embedded videos, only sound, no video, however at end of video the last frame (still image) suddenly appears. Now, am also getting some You Tube videos with video, but NO audio. The same videos playing fine in Internet Explorer, so this is clearly a specific Firefox problem. I searched for resolution, finding out of date garbage from 5 years ago. I tried reinstalling Adobe Flash player, no fix. Reinstalling Shockwave Flash player, no fix. Tried disabling ALL add ons, extensions, plug ins, NO fix. Tried Flash Control extension, no fix. Finally, a You Tube Flash player extension seem to work, video does eventually play. But not until after error messages appear such as - "A plug in is needed to display this content." and - " Your browser does not currently recognize any of the video formats available." WHAT is necessary to resolve this so that videos and audio play properly, without errors and error messages? * Adobe PDF Plug-In For Firefox and Netscape 15.10.20056 * AlternaTIFF v2.0.7 * DivX Web Player version 3.5.5.3 * DivX VOD Helper Plug-in * Google Update * Intel web components for Intel® Identity Protection Technology * Intel web components updater - Installs and updates the Intel web components * NPRuntime Script Plug-in Library for Java(TM) Deploy * Next Generation Java Plug-in 11.66.2 for Mozilla browsers * NPWLPG * Shockwave Flash 21.0 r0 * Adobe Shockwave for Director Netscape plug-in, version 12.2.2.172 * Yahoo Application State Plugin version 1.0.0.7