A easy way to see if you can play HTML5 videos in Firefox is to go to https://www.youtube.com/html5/ as they should be all blue check marks.

Since you have the old EOL WinXP and not Vista or later you may not be able to play HTML5 without some workarounds.

With some workarounds you may be able to. http://www.msfn.org/board/topic/175591-enable-mp4-h264-aac-html5-video-in-firefox-on-windows-xp-without-flash/

Also VLC with its Plugin may help. http://www.videolan.org/vlc/index.html

I've been getting MEDIA COULD NOT BE PLAYED on Twitter videos. I have the latest version of Firefox on Win. 10 I contacted tech support and uninstalled Adblock Plus, tried Adblock. Still the videos did not play. Only when I uninstalled all Adblock did it work. It could be a bug or incompatibility with Firefox, as I tried it with Edge and the videos worked.

Hi Leebossa

Firefox needs native support on the operating system level to play MP4 files with the HTML5 media player. The original poster is on XP and thus won't have this support.

On other Windows versions this should work unless your Windows version lacks this support. See also:

• https://support.mozilla.org/en-US/kb/fix-video-audio-problems-firefox-windows
• https://support.mozilla.org/en-US/kb/fix-common-audio-and-video-issues

thank you, I'm not sure exactly if that's the situation. I should point out it only refers to videos, not music, i/e news videos.

I just had a windows update but I will check to see if I have the media feature pack installed.

So you don't see it as being a problem with adblock or related to that at all?