Enable HTML5 video support on YouTube in Firefox

While the Firefox has a very good support for HTML5 standards, you may have noticed that it doesn't support all of them characteristics required to play YouTube videos without Adobe installed Flash Player. It does support the required HTMLVideoElement attribute, but some videos won't play anyway. Why is this happening;

These videos require this feature to be disabled by default on the Firefox page with Media Source Extensions. By default, this option is disabled by Firefox developers, so the popular browser is unable to play HTML5 video streams. To enable the feature, follow these steps:

Open your Firefox browser and type it in the address bar below:

about: config

Note: A window will appear with a rather humorous dialog-pronotice. "Προσοχή! Μπορεί να ακυρώσετε την εγγύηση του productτος" . Καλό ε; Μη φοβηθείτε οι προγραμματιστές του δημοφιλούς προγράμματος περιήγησης σας κάνουν πλάκα...

Of course, it's a good idea to know what you are doing before you start to change the values ​​on the settings page.

Κάντε κλικ στο "Θα είμαι προσεκτικός, το υπόσχομαι!" για να συνεχίσετε.
Πληκτρολογήστε τη λέξη"MediaSource" (χωρίς τα εισαγωγικά που χρησιμοποιούμε εμείς) στο πλαίσιο αναζήτησης

You will see the media.mediasource.enabled parameter set to false. Double click on it to change its value to true.

Restart Firefox to enable the feature.

Now open some of the YouTube videos that are in HTML5 and were not originally played. They should play without problems.