Some of those sites use an open source player (I forgot the name). They actually changed the default priority order and put Flash first, so if Flash is installed (not necessarily enabled!) it will use Flash in favor of HTML5.<p>Firefox used to have an option that overwrites the list of plugins reported to JavaScript. Sadly it was disabled a few versions back.<p>Edit: The player is Projekktor [0], the FF setting was plugins.enumerable_names [1]. There&#x27;s a new option coming that hides plugins when set to click-to-play [2]<p>0: <a href="https:&#x2F;&#x2F;github.com&#x2F;frankyghost&#x2F;projekktor" rel="nofollow">https:&#x2F;&#x2F;github.com&#x2F;frankyghost&#x2F;projekktor</a><p>1: <a href="https:&#x2F;&#x2F;bugzilla.mozilla.org&#x2F;show_bug.cgi?id=1169945" rel="nofollow">https:&#x2F;&#x2F;bugzilla.mozilla.org&#x2F;show_bug.cgi?id=1169945</a><p>2: <a href="https:&#x2F;&#x2F;bugzilla.mozilla.org&#x2F;show_bug.cgi?id=1186948" rel="nofollow">https:&#x2F;&#x2F;bugzilla.mozilla.org&#x2F;show_bug.cgi?id=1186948</a>