Microsoft only provides media feature packs that has the needed codescs to fully use the HTML5 player on Windows Vista, 7, 8, 10 but not to WinXP users.

You can see what you can support with HTML5 player at say https://www.youtube.com/html5/ as all check marks should ideally be blue.

Not sure if this guide for WinXP will work anymore. http://www.msfn.org/board/topic/175591-enable-mp4-h264-aac-html5-video-in-firefox-on-windows-xp-without-flash/

Chrome/Chromium (and Opera) has not supported the EOL WinXP/Vista since April 2016. Chrome comes with its own codecs (cheating of sorts) as to why the old vulnerable Chrome version you have (before Chrome 50.0) may be able to more fully play HTML5 videos on WinXP.

Hi

All that about:config fiddeling did it :-) Do i have to jump those hoops every time you send out an update from now on???

Thanks for the help and have a nice day Henrik

I like most of the mods here do not work for Mozilla.

Unless otherwise most Preference changes do not get changed after a new update or install.

How to get HTML5 video to play in YOUTUBE if it is "oddly incompatible with your browser". ADD to your ADBLOCKER. (copy & paste). |https://www.youtube.com/yts/jsbin/*/spf.js |https://www.youtube.com/yts/jsbin/*/www-pagead-id.js

I got a HTML5 video incompatibility fake error from YOUTUBE and am now watching HTML5 videos in the same Firefox 52.6 (garbage quality) browser after ADBLOCKING these parts of Youtube's defective webpages. It isn't your browser that is broken (except by stupidity on the programmer's part), it is YOUTUBE using this technique to censor videos.

matrix29bear, sorry this is belated, but can you please clarify - if I have Win-XP and getting the same error msg as the OP - am I supposed to:

(1) download HTML5 from somewhere? (where from?)

(2) then paste above codes to ADBLOCKER? (where's that?

Thanks.