I-Firefox Community Forum

(AI written summary of troubleshooting steps taken before making this support thread)

Firefox version: - 152.0.1 Release - 153.0 Nightly

OS: - Windows 11 build 26200

GPU: - NVIDIA GeForce RTX 4070 SUPER

Codec package: - Microsoft HEVC Video Extensions installed from Microsoft Store

Problem

Firefox does not expose HEVC playback support, causing Twitch to disable 1440p streams encoded with HEVC.

The same machine can play the same HEVC Twitch streams in Chrome immediately after installing HEVC Video Extensions.

Expected result

Firefox should report HEVC playback support and allow playback of HEVC streams, as Chrome does on the same system.

Actual result

Firefox reports HEVC as unsupported.

about:support:

codecSupportInfo: H264 SWDEC HWDEC VP9 SWDEC HWDEC VP8 SWDEC HWDEC AV1 SWDEC HWDEC HEVC NONE

Troubleshooting already performed

- Installed Microsoft HEVC Video Extensions - Rebooted Windows - Updated NVIDIA drivers - Verified hardware acceleration is enabled - Tested with a brand new Firefox profile - Tested with Firefox Nightly - Confirmed Chrome can play the same HEVC streams

Additional observations

Chrome: - Twitch 1440p becomes available immediately after installing HEVC Video Extensions - Twitch Stats for Nerds reports:

 hev1.1.6.L150.90.0.0.0.0.0

Firefox: - Twitch reports that the browser does not support the required resolution - 1440p remains greyed out - about:support continues to report HEVC NONE

Reproducible tests

Firefox console:

MediaSource.isTypeSupported('video/mp4; codecs="hev1.1.6.L150.90"')

Result: false

MediaSource.isTypeSupported('video/mp4; codecs="hvc1.1.6.L150.90"')

Result: false

navigator.mediaCapabilities.decodingInfo({

 type: "media-source",
 video: {
   contentType: 'video/mp4; codecs="hev1.1.6.L150.90"',
   width: 2560,
   height: 1440,
   bitrate: 8000000,
   framerate: 60
 }

})

Result: {

 supported: false,
 smooth: false,
 powerEfficient: false

}

For comparison:

MediaSource.isTypeSupported('video/mp4; codecs="av01.0.08M.08"')

Result: true

navigator.mediaCapabilities.decodingInfo({

 type: "file",
 video: {
   contentType: 'video/mp4; codecs="av01.0.08M.08"',
   width: 2560,
   height: 1440,
   bitrate: 8000000,
   framerate: 60
 }

})

Result: {

 supported: true,
 smooth: true,
 powerEfficient: true

}

Additional note

Setting:

dom.media.webcodecs.h265.enabled = true

causes HTML5 codec test (https://html5test.co/) to report H.265 support, but does not change:

- about:support - MediaSource.isTypeSupported() - MediaCapabilities.decodingInfo() - Twitch HEVC playback availability

Question

Is this a known issue with HEVC Media Source Extensions support on Windows 11 build 26200, or is there another requirement for Firefox to expose HEVC playback capability through MediaSource and MediaCapabilities when the Windows HEVC codec is installed and functioning in Chromium-based browsers?

Trouble with streaming services(like youtube(only streams ), twitch, music streaming) on nightly Firefox Nightly 145.0a1 (2025-10-11) (x64) Cachy OS Binary from firefox.com

Quality switches to 360 when tab inactive firefox. I watch Twitch in 1080p. When I switch to another tab and then return, the quality drops to 360p and then automatically goes back to 1080p.

how to cast videos from my phone to my TV if I got android phone, and I have i basic Sylvania TV without wifi or Bluetooth connection, hmi and a softwaode with fire fox app.link text

Здравствуйте. При воспроизведении видео на каком либо сайте в полноэкранном виде не скрывается панель задач виндовс. На других браузерах работает как надо. Менял где только можно, даже в безопасном режиме также. Как её можно убрать?

I am using Pop OS. Videos are not playing in firefox. In youtube it shows loading infinitly. In reddit all videos become green. I tried playing a downloaded video it also become green. These are only happening in integrated mode. If I use hybrid graphics mode all works good. I attached the about:support page and about:config page.

about:config page link about:support page

These files are taken in integrated graphics mode.

I am do not get sound using audio recorded with akamai player with Fire Fox browser. I tried the same link using Edge browser and the audio works.

I have tried clearing the cache, but still no sound.

How do I resolve this issue using Fire Fox as my default browser? Is there an audio extension that is needed?

So, my problem is with HW acceleration in FF. Basically:

If its enabled: It causes graphical artifacts in videos [See screenshot]. If its disabled: It brings screen tear in to videos and autoscroll [Like if Vsync is disabled in games].

I tried safe mode, I tried reinstall of FF, I tried disabling and enabling extensions. I tried to set Vsync on in Nvidia control panel... the only thing that impact those bugs is HW acceleration in FF.

My drivers are up to date, my browser is up to date, yet there is such trouble.

Any ideas or solutions?

I think everyone knows how to get out of full screen mode by now, so can you either remove it or let us disable that little box that always shows when you go full screen for a video?

Hello, I am facing an issue while playing YouTube videos in Firefox. The videos are lagging and not playing smoothly, even though my internet connection is fine. Please help me fix this problem.

Since to your "upgrade"to firefocx on my computer I can no longer watch youtube or iplayer videos. Pease say how I can downgrade my version so as to be able to see these.

Hello, I am currently using windows 11 with firefox 149.0. Regardless of what website I use (youtube. steam etc), the browser struggles to establish consistent connection to my bluetooth earbuds. It connects for one moment, but then soon the volume goes out and eventually it disconnects. Though it would reconnect soon, the cycle just keeps ongoing. I have experimented with other apps and browsers, as well as multiple bluetooth earbuds of other brands to be sure that it is a firefox issue. I have checked the volume mixer menu to ensure that there is nothing wrong. I have also made sure that my drivers are all up to date with no issue. But the issue still persists.