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Youtube videos not loading using Firefox


I recently started having a problem using firefox with youtube. I installed the Tamper Data add-on and restarted. After I restarted no youtube videos would load. They just sit with a black screen. I've tried clearing all cookies and restarting firefox. I've also tried disabling the Tamper Data extension but it does nothing. I updated adobe flash player as well. This does not happen on any other flash-based websites. All youtube videos work perfectly in IE and chrome. Thanks.

Additional System Details

Sites Affected


Installed Plug-ins

  • Shockwave Flash 10.2 r152
  • NPRuntime Script Plug-in Library for Java(TM) Deploy
  • Adobe PDF Plug-In For Firefox and Netscape "9.4.0"
  • Default Plug-in
  • The QuickTime Plugin allows you to view a wide variety of multimedia content in Web pages. For more information, visit the QuickTime Web site.
  • Google Update
  • iTunes Detector Plug-in
  • Next Generation Java Plug-in 1.6.0_22 for Mozilla browsers
  • 4.0.50917.0
  • Office Authorization plug-in for NPAPI browsers
  • The plug-in allows you to open and edit files using Microsoft Office applications


  • User Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US; rv: Gecko/20101203 Firefox/3.6.13

More Information

Question owner

I downloaded firefox 4 beta 11 and it seems to work fine. Apparently it has something to do with the old version not supporting some codec used with HTML5 on youtube.