Am using Firefox 80.0.1 (newly updated) and Linux Mint 18.3. I have a problem with HTML5 and also codecs problems on at least two other sites (my daily newspaper and The Register). The problem existed even in the previous Firefox version. If I use Chromium these videos work. The newspaper problems give the message that the browser can't play any of the available formats - code 12. I checked the web console ans there were many messages. I had logging allowed and set to the clipboard (gpaste) but nothing turned up there. I did a screen shot which is a png. I copied the results here. Missing codecs video/mp4; cidecs="avc1.42E01E mpra.40.2". This works in Chromium. As far as I understand HTML5 should work in Firefox. I've seen 2 places where it doesn't: live streaming from World Science Festival and from metopera.com. I've seen the problem once on youtube however I could view the same video later with no problem. As for the missing codecs I can live with using Chromium in the 2 cases the problem has shown up. But I would like some clarification on the HTML problem.