YouTube videos started playing after I installed Adobe Flash. Without Flash most of Firefox vidoes just don't play. e.g. https://www.youtube.com/watch?v=TpN7wHFV9nc&feature=youtu.be Amazon Prime Video doesn't work either (didn't test with Flash - just use Chrome for that). But some Twitter videos didn't play even with Flash. e.g. https://twitter.com/indiannavy/status/855763874586513410. Do I need another plugin for this? Audio - I didn't keep specific record of this (will update this question) but some sites like Soundcloud mostly works and some sites like gaana.com upfront ask for Flashplayer to be installed but other sites mostly just go silent - no sound, no prompt, no error. No, I checked it's not happening because of some extension - tested it in Safe Mode too and also with just disabling uBlock Origin. Yes, I am aware of Firefox going ballistic on Flash and many plugins (and rightly so) post 52 (other than in Extended Support) but how, in general, to figure out, when media content doesn't play, that I need something else to to play that content? I don't even see any "something disabled" or "some plugin or some kind of support required" button either. Error screenshots for Youtube and Twitter attached.