How to enable MSE & H2.64 support on YouTube for Firefox right now

When you open YouTube's HTML5 page in the most recent stable version of Firefox right now, you will notice that support is not available for all technologies listed on the page.

Support may be available for HTMLVideoElement, H.264 and WebM VP8, but not for Media Source Extensions, MSE & H.264 or MSE & WebM VP9.

A configuration option is available to enable Media Source Extensions and MSE & WebM VP9 right now in the Firefox browser.

To do so, load about:config in the browser's address bar and search for the term media.mediasource.enabled there. Double-click the preference to set it to true.

When you go back to YouTube's HMTL5 page afterwards, you will notice that only MSE & H.264 is listed as unsupported while all remaining options are supported.

firefox mse support

If you do not do that, you will only receive select resolutions for videos on YouTube when using the HTML5 video player. This is quite problematic as Google will force Firefox users to use the HTML5 video player from Firefox 33 on.

Mozilla has not enabled the feature by default yet, not even in the most recent Nightly version of Firefox. This is an indicator that the feature is not yet ready for prime time and that it may take a couple of release cycles before it will be enabled by default.

Most video resolutions become available after you enable Media Source Extensions in Firefox. What is still not supported afterwards however is MSE & H.264 which means that some videos may not play in all resolutions yet on the site.

Enable MSE & H.264

A new preference in Firefox Nightly 34 changes that however, so that support for all requested technologies is provided afterwards on YouTube.

Note: While the article concentrates on Google's video hosting platform, enabling support for MSE & H.264 will benefit users of the browser on other websites as well.

You need to create a new preference to do so:

  1. Type about:config and hit enter.
  2. Confirm you will be careful.
  3. Right-click and select New > Boolean.
  4. Name the preference media.mediasource.ignore_codecs.
  5. Set its value to True.

Update: Linux userrs may change the following preferences as well:

  1. media.mediasource.mp4.enabled to true
  2. media.fragmented-mp4.* to true
  3. media.fragmented-mp4.use-blank-decoder to false

If you go back to YouTube's HTML page, you should see all six technologies listed as supported (in green).

firefox mse h264 support

Several bugs need to be resolved before the feature will be enabled directly by Mozilla for all users of the browser. You can check out the mediasource progress here.

This means that you may get hangs or experience other issues after enabling mp4 container support for Media Source Extensions in the browser.

Still, it is great to see that Mozilla is working on support for the feature in Firefox. It is unclear if it will manage to resolve all issues before Firefox 33 gets released, as it may result in an increase in support requests when Firefox users notice that YouTube is serving them only some resolutions.

Article Name
How to enable MSE & H2.64 support on YouTube for Firefox right now
Mozilla has enabled support for H.264 Media Source Extensions in Firefox 34. Find out how to enable the feature in Firefox right now.
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Responses to How to enable MSE & H2.64 support on YouTube for Firefox right now

  1. EuroScept1C July 25, 2014 at 4:56 pm #

    Right now best way to see videos on Youtube: IE11 and go to Safety-> ActiveX Filtering and enable it. It will play ALL videos on mp.4 format with DASH enabled, 1080p support and all. The most efficient way.

    • Rofl October 17, 2014 at 8:54 am #

      IE, are you crazy?

      • Lofty November 1, 2014 at 8:50 am #

        Software has no opinion. Only people do. Such as yours.

    • lofr February 9, 2015 at 2:16 am #

      install user agent switcher and set it to IE 11

  2. pd July 25, 2014 at 7:54 pm #

    Running Aurora on Windows XP, I still don't have the Cisco h.264 codec. Any way to enable that?

    • Martin Brinkmann July 25, 2014 at 8:07 pm #

      Not yet, it appears to be only available in Nightly right now.

  3. geeknik July 26, 2014 at 1:27 am #

    MSE on YouTube still doesn't work properly. Seeking sometimes takes a lot of time, seeking back doesn't work at all and repeat also doesn't work. Just because you can flip the switch doesn't mean you're going to get MSE & H.264 support because according to a Mozilla developer, MP4 (H.264, etc.) aren't supported in MSE yet. They are concentrating on Webm on YouTube right now.

    Relevant bugs:,

    My advice, don't force enable MSE for now unless you want a lot of YouTube headaches. ;)

  4. marius t July 26, 2014 at 9:48 am #

    No thanks I'll still use flash untill it really dies,my motto if it works don't mess with it!I'll force flash player with Youtube Center if I have to!

  5. Aramir September 1, 2014 at 10:47 am #

    I did that and lost sound on youtube videos .... No thanks

    • vita December 20, 2014 at 11:34 am #

      i lost sound too. how to fix it?

  6. bedsitter September 19, 2014 at 8:54 pm #

    I've done this under Firefox 32.02, but MSE & H.264 is still signed red.
    Don't know why this works for the author...

    • Petre September 22, 2014 at 12:26 am #

      It's the same for me under Ubuntu

  7. pd October 30, 2014 at 1:46 pm #

    The CISCO h.264 codec is in my plugin list now.

    I've added the media.mediasource.ignore_codecs true boolean

    On this page:

    only HTMLVideoElement and WebM VP8 are available.

    So I've got a CISCO h.264 codec, the Flash plugin would have h.264 support, but YouTube thinks I can't play h.264 videos. WTF? :)

    I'm keen to get rid of the crappy Flash plugin if I can finally use the HTML video tag with the CISCO h.264 codec.

    • Martin Brinkmann October 30, 2014 at 2:23 pm #

      The Cisco plugin is currently only being used for WebRTC as far as I know.

  8. pd October 30, 2014 at 2:29 pm #

    Ah nuts. Flipping Mozilla sure know how to make life hard on their users!

  9. Jay November 15, 2014 at 1:01 am #

    MSE works fine as far as I can tell. But I can see why they hid "ignore_codecs" from the config page. 1080p playback just stops playing randomly, and 720p keeps glitching, freezing, and occasionally the audio stops working. Hope Mozilla can sort this out soon as I really want to play 60fps in Firefox. For now I have to use 'youtube-dl -g' to grab the URLs for 60fps streams so I can watch them in VLC, or open Chrome.

    Firefox Developer Edition 35.0a2 (2014-11-14)

    EDIT: Slight correction. With MSE enabled, some 60fps videos do work with FF as they have WEBM 60fps streams, but playback is sporadic/laggy and not very watchable. Chrome plays the same videos fine at 60fps so it's not my PC's fault.

  10. Hisham January 5, 2015 at 7:53 pm #

    Thank you :)

  11. Remi January 7, 2015 at 1:23 pm #

    Do not add the value to ignore codecs in "about:config". You'll lose sound in Youtube-Videos !

  12. Marc Aurel February 14, 2015 at 4:16 pm #

    Running FF 35.01 in Windows 7 and MSE still doesn't work properly. Sound is sometimes lost and seeking back does not work, so no change from earlier, although Mozilla claims most of the bugs fixed now. Perhaps the nightly builds would work.

    Enabling MSE also causes Youtube to offer VP9 streams to FF by default, which means that you will lose hardware acceleration with most GPUs. That happens even with "ignore_codecs" enabled. With a modern CPU that is not a problem, but it certainly is on my secondary system with an older processor. 720p is choppy and 1080p is a slide show.

    • Jay February 14, 2015 at 4:28 pm #

      MSE is working near flawlessly in FF37, so it'll trickle down soon. I have none of the issues you mention in the latest DE build.

      PS: You can disable WebM support by disabling the following flag: "media.mediasource.webm.enabled"

      • Marc Aurel February 16, 2015 at 3:02 am #

        Thanks for your answer. Good to know that it's improving. Do you know if they are going to enable MSE by default in FF37?

    • Jay February 16, 2015 at 7:24 am #

      Seems the plan is to have MSE enabled in FF36, but limited to Youtube and only Windows 7+(maybe Mac as well). It seems they are still having issues with MSE+MP4 on Linux, and MSE+WEBM still isn't completely ready. Seems full MSE support will hit in FF37, but EME doesn't seem ready yet so support for services like Netflix will likely still be awhile.

      NOTE: This is what I've gathered by reading the Bug Tracker, but there are hundreds of different bugs and issues being tracked related to MSE and EME making it hard to be sure, so things could always be delayed.

  13. hugh April 1, 2015 at 5:27 am #

    Hi Martin,

    I'm missing something here about the youtube html page.

    I've managed since taking the screenshot to to enable the MSE & WebM VP9 after finding an older post of yours.

    However The remaining two H.264 and MSE & H.264 still have the red exclamation marks.

    Any advice appreciated,


    • Martin Brinkmann April 1, 2015 at 8:23 am #

      Which operating system are you using?

      • hugh August 15, 2015 at 12:22 am #

        Sorry for the delay

        Current OS = Windows 10 Pro.
        I think when I first posted it was Windows 8.1 Pro - but the youtube html page still shows the same information as in the originally posted screenshot.



  14. Claymore April 1, 2015 at 3:27 pm #

    I thought, I'll post my frankenstein-solution for smooth 1080p videos @60FPS at Youtube here:

    Firefox: 37.0
    Clean Profile: Yes
    Used OpenH264 Version: 1.3

    System specs:
    Q6600 @3.0Ghz
    8GB DDR2 RAM
    Club3D 7870 JokerCard

    Following settings are changed for it:
    media.fragmented-mp4.ffmpeg.enabled: true
    media.fragmented-mp4.gmp.enabled: true true

    Tested video:

    Yes, "MMSE & WebM VP9" won't get enabled, but doesn't really matter in this case.

  15. Kurt May 5, 2015 at 3:56 pm #

    This doesn't work anymore. media.mediasource.enabled is already true in 37.0.2, and adding ignore_codecs does nothing.

    Youtube only offers 360p as an option.

    • Jay May 5, 2015 at 6:55 pm #

      MSE is enabled by default in FF37. Youtube videos should play with DASH support now. If they aren't for you try making sure "media.mediasource.mp4.enabled" and "media.mediasource.webm.enabled" are both set to true. Also make sure "media.mediasource.whitelist" is set to false if you want to use non-Youtube sites with MSE, though it should already be disabled in FF37.

      If you are still having issues, what OS are you running? Are all of the boxes checked on ?

      • Kurt May 5, 2015 at 11:40 pm #

        Setting "media.mediasource.webm.enabled" to true fixed it. Thank you!

        MSE & H.264 and H.264 are red, but I can choose the quality now.

      • Einar ├ôlafsson September 24, 2015 at 8:05 pm #

        Excellent addition to the tutorial, this fixed my last issue on getting "MSE & WebM VP9" checked of the list of supported features. I'm running a stable build (40.0.3) on Fedora 22.

    • Jay May 6, 2015 at 12:31 am #

      Sounds like there is something wrong with MSE MP4 support for you then. Are you running Mac or Linux? That could be part of the reason.

      • Kurt May 6, 2015 at 11:42 am #

        EDIT: I just fixed it by setting "media.fragmented-mp4.enabled" to true. I'm using Windows 7, but this was in your Linux only users section.

        Now everything on the youtube HTML5 page is ticked.

  16. Set Elrich May 6, 2015 at 11:39 pm #

    I followed the instructions, and nothing changed. :/

  17. datruche September 17, 2015 at 10:05 pm #

    Firefox 40.0.3 on Win XP SP3: All is red on Youtube html5 test page, ie does not work.

    Intel Graphics GMA500 "Poulsbo": Hardware acceleration on.
    CCCP installed and configured with both filters (MPEG4 Video (H264) 720x576 plays fine in mpc)
    Firefox: media.directshow.enabled;true && media.hardware-video-decoding.enabled;true && media.mediasource.mp4.enabled;true && media.fragmented-mp4.enabled;true && media.mediasource.webm.enabled

    Looks like there's no H264 support in Windows XP. That's what is said in these places:

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