Hi   ! YouTube only uses an HTML5 video player and dropped Flash formats.

YouTube videos may be in a format that Firefox can't decode on Windows XP (H.264/MP4), for Firefox requires the Microsoft Media Foundation, which Microsoft only released it for Vista and later versions.

Google transcodes videos to other formats in the background, so eventually a playable format will be available.

This might be a workaround for Firefox 52 ESR on Windows XP :

http://www.msfn.org/board/topic/175591-enable-mp4-h264-aac-html5-video-in-firefox-on-windows-xp-without-flash/

Any good  ?

I followed the link you posted and it took me to post way down in a thread, so I went with that and followed the instructions and readded

media.gmp-eme-adobe.visible media.gmp-eme-adobe.enabled

in about:config

set both to TRUE.

made no difference still same error.

I would love to play about with fixing this problem with Firefox but have much more I need to get on with and unfortunately will uninstall Firefox and start using Google Chrome since it plays all my YouTube videos without a hitch.

I guess that's why they made the changes over at Google, to YouTube, and it has worked!

One more thing, I do have the HTML5 addon / plugin so I'm not sure what you're meaning by

"YouTube only uses an HTML5 video player and dropped Flash formats"

There is more needed apart from the two prefs you posted to make Firefox use the OpenH264 plugin.

This involves modifying some preferences on the about:config page. media.gmp-eme-adobe.enabled (boolean, true) media.gmp-eme-adobe.forceSupported (boolean, true; FF 49.0+) media.gmp-eme-adobe.forcevisible (boolean, true; FF 45-48, no longer used in 49.0+) media.gmp-eme-adobe.visible (boolean, true; FF 49.0+) media.gmp.decoder.enabled (boolean, true) media.eme.enabled (boolean, true)

Modify media.gmp-manager.url : change %VERSION% to 51.0 (use 46.0 for Firefox 45 ESR)

Firefox 52.xx ESR users need to remove the Primetime plugin if it is currently loaded. You can delete the gmp folders (gmp and gmp-gmpopenh264) in the profile folder.

• Help -> Troubleshooting Information -> Profile Directory: Windows: Show Folder

If you use any extensions that used to force Flash on YouTube, please uninstall them, they are obsolete now and may interfere with using the site. For example:

• YouTube Flash Player
• YouTube Flash Video Player

You can view, disable, and often remove unwanted or unknown extensions on the Add-ons page. Either:

• Ctrl+Shift+a (Mac: Command+Shift+a)
• "3-bar" menu button (or Tools menu) > Add-ons
• type or paste about:addons in the address bar and press Enter/Return

In the left column of the Add-ons page, click Extensions. Then cast a critical eye over the list on the right side. Any extensions that Firefox installs on its own are hidden from this page, so everything listed here is your choice (and your responsibility) to manage. In addition to either of the ones I mentioned, if you use any video downloaders or recorders that force Flash, try disabling those.

Often a link will appear above at least one disabled extension to restart Firefox before the change takes effect. You can complete your work on the tab and click one of the links as the last step.

Any improvement?

Another thing to try :

Set the VLC media player Web Plugin to   'Never Activate'

It worked,

I did everything listed above , the last thing that I did before it worked was was set Primetime to never active, because I couldn't work out how to delete it.

Then my video's played

Thanks guys

Correction I didn't delete the right folder with gmp and gmp-gmpopen264, they are still there

I deleted another folder on the program files-mozilla-- gmp

so i messed up slightly

Storio said

so i messed up slightly

No, you didn't mess up at all   - you did a great job   ! I think setting the Primetime plugin to "'Never Activate' is what did it. Well done   !

As it was cor-el who suggested you'd do that : Would you be a dear and mark cor-el's post as   'Chosen Solution'  ?
That way others, with the same problem, will know and might beneft from it.

Thank you in advance   !

I have 2 computers with exact same spec (1 now fixed) and with the same issue, so I will attempt to fix the second one but will do everything in the reverse order and see at what point it rectifies.

Good News Bad News

On my quest to fix my above mentioned issue I also came across a very recent post that stated that the issue was related to YouTube requiring channels to monetization themselves. I did monetization but didn't think it was relevant since my channel would have needed lots of hits to get to the threshold for monetization to occur.

However I yesterday received an email saying my channel was eligible and set up for monetization, around the exact time I was implementing those changes to my FireFox configuration set up.

When I went to my second computer I thought I would check out the possibility that the monetization of my YouTube channel was in fact the fix.

So I did none of the changes, as listed above, and just found my channel and low and behold it played my videos with no problem at all.

Previously this second PC had the exact same fault with the same error message as my first PC. So my logic is now shaken on what the exact fix is in this situation.