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Why does video stutter in Firefox?

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When I watch video in Firefox it stutters badly. I have tried disabling hardware acceleration in Adobe Flash Player. I have also tried uninstalling Firefox and re-installing a clean copy but I still have this issue.

Chosen solution

Try to disable Protected Mode in Flash 11.3 and above by adding the line ProtectedMode=0 to the Flash "mms.cfg" file located in one of these locations: [46]

   (Windows 32bit) C:\Windows\System32\Macromed\Flash 
   (Windows 64bit) C:\Windows\SysWOW64\Macromed\Flash 

For example, on a Windows 7 64-bit system, open the C:\Windows\SysWOW64\Macromed\Flash folder, copy the file "mms.cfg" to the desktop, open it in Notepad, add a new line ProtectedMode=0 and then close Notepad, saving your changes. Next, go back to the C:\Windows\SysWOW64\Macromed\Flash folder, rename the original file to "mms.cfgBAK" (to save it as a backup) and then drag and drop in the modified "mms.cfg" file from the desktop. [47] [48] [49]

Note: To re-enable Flash Protected Mode, either restore a backup of the original mms.cfg file, if you saved one, or else re-edit the mms.cfg file to remove the ProtectedMode=0 l line you added. Updating Flash Player or installing a newer version does not automatically re-enable Protected Mode

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Chosen Solution

Try to disable Protected Mode in Flash 11.3 and above by adding the line ProtectedMode=0 to the Flash "mms.cfg" file located in one of these locations: [46]

   (Windows 32bit) C:\Windows\System32\Macromed\Flash 
   (Windows 64bit) C:\Windows\SysWOW64\Macromed\Flash 

For example, on a Windows 7 64-bit system, open the C:\Windows\SysWOW64\Macromed\Flash folder, copy the file "mms.cfg" to the desktop, open it in Notepad, add a new line ProtectedMode=0 and then close Notepad, saving your changes. Next, go back to the C:\Windows\SysWOW64\Macromed\Flash folder, rename the original file to "mms.cfgBAK" (to save it as a backup) and then drag and drop in the modified "mms.cfg" file from the desktop. [47] [48] [49]

Note: To re-enable Flash Protected Mode, either restore a backup of the original mms.cfg file, if you saved one, or else re-edit the mms.cfg file to remove the ProtectedMode=0 l line you added. Updating Flash Player or installing a newer version does not automatically re-enable Protected Mode

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Thanks! That worked with the exception of the fact that I had to copy the .cfg file to the desktop (as you explained) and then after making the changes, I had to save the file to a different folder, delete the original mms.cfg file from the C:\Windows\System32\Macromed\Flash folder. Then I was able to drag it from the new folder into the Flash folder and it all worked good. I also restarted Firefox just to ensure it would work.