If your Firefox browser doesn’t play videos in youtube or any other flash content please follow the steps below to fix the issue.Go to adobe website https://get.adobe.com/flashplayer/ and download the flash player file with name ending .tar.gz.
Extract the downloaded tar.gz file by tar -zxvf filename.tar.gz
It will create a file called libflashplayer.so (See above screenshot). Then copy that file to users home directory/.mozilla/plugins folder.
Restart firefox.
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