Enable 1080p YouTube Support in Firefox 40 for Linux

"You can check if your browser supports all the codecs for YouTube by checking the YouTube HTML5 Video Player website, which list everything supported on your PC. If you have a Linux systems and Firefox 40, it's likely that some of those codecs will have a red sign, meaning that they are not enabled. All you have to do is open about:config and make the following changes. Please make sure that you don't change anything else. ..."
Source: Softpedia
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