Firefox 160 is out, and it now plays MKV videos with FLAC, MP3 and PCM audio - here is what plays, what still doesn't, and the quick fix for the rest.
Mozilla released Firefox 160 this week, and the update is rolling out to Windows now.
The headline change for video fans is wider MKV support, plus a new Mini Window and speed controls in picture-in-picture.
If an MKV still won't play, the cause is usually its audio track, and a free player sorts it out in a minute.
What's New in Firefox 160 for MKV Files
MKV is a "container" - a box that holds a video track, one or more audio tracks and sometimes subtitles. Whether a file plays depends on what's inside the box, not on the .mkv name.
Firefox learned to play MKV in version 145, a year ago, but only with certain audio. Firefox 160 adds three more audio types, so many music videos, concert rips and home recordings now play too.
| Inside the MKV | Plays in Firefox 160? |
|---|---|
| Video: H.264, HEVC, VP8, VP9, AV1 | Yes (since Firefox 145) |
| Audio: AAC, Opus, Vorbis | Yes (since Firefox 145) |
| Audio: FLAC, MP3, PCM | Yes - new in Firefox 160 |
| Audio: Dolby Digital (AC-3, E-AC-3), DTS, TrueHD | Not on Mozilla's list - use a media player |
| Subtitles built into the MKV (SRT, ASS) | Not supported - use a media player |
Where this helps most.
Websites that serve MKV videos now just work in Firefox, without asking you to download the file first. It is a browser feature, not a full media player.
How to Get Firefox 160
- Check your version. Open the menu, then Help > About Firefox - it downloads the update and asks you to restart.
- No update yet? Mozilla rolls updates out over a few days, so grab the latest Mozilla Firefox installer instead.
- Try an MKV. Open a page with an MKV video, or drag an MKV file from your PC into a new tab.
MKV Still Won't Play? The Two-Minute Fix
If Firefox shows a blank player, plays video with no sound, or offers to download the file, the MKV almost certainly carries Dolby, DTS or TrueHD audio. Films ripped from Blu-ray or DVD usually do.
A browser is the wrong tool for those files anyway. A free desktop player handles every track, plus the built-in subtitles Firefox ignores.
- VLC Media Player - plays almost any MKV straight away, with every audio and subtitle track in the menus. Nothing else to install.
- K-Lite Codec Pack - adds the missing decoders to Windows, so MKV files play in Media Player Classic, Windows Media Player and other apps too.
Not sure what's inside your file?
Open it in VLC and go to Tools > Codec Information. If the audio line says A52 (that's AC-3), DTS or TrueHD, Firefox won't play it - VLC will.
The Other New Features Worth Knowing
- Mini Window (beta). Right-click a tab and choose Move Tab > Move to Mini Window to keep it floating on top while you work - handy for a video, a chat or a recipe.
- Move just part of a page. Right-click and pick Move Section to Mini Window, then draw around the bit you want to keep in view.
- Picture-in-picture speed. Pop a video out into picture-in-picture and you can now set the speed from 0.25x to 2x - the button appears once the window is medium-sized or larger.
- Speech-to-text for websites. Sites can now turn your voice into text in 40 languages, and Firefox does it on your own computer rather than sending the audio away.
Quick questions
Can Firefox play MKV files?
Yes, since Firefox 145. Firefox 160 adds FLAC, MP3 and PCM audio, so most MKV files with common video and audio now play.
Why does my MKV have no sound in Firefox?
The audio is probably Dolby Digital (AC-3), DTS or TrueHD, which Firefox doesn't list as supported. Play the file in VLC instead.
Does Firefox show MKV subtitles?
No. Subtitles built into an MKV aren't shown. VLC and Media Player Classic display them and let you switch between tracks.
How do I update to Firefox 160?
Open the menu, then Help > About Firefox, and restart when it asks. You can also download the latest installer and run it over your current version.
What is Mini Window in Firefox?
A new beta feature that moves a tab, or part of a page, into a small window that stays on top of everything else.
The bottom line
Firefox 160 plays far more MKV files than before, which makes MKV videos on websites much less of a headache. For films with Dolby or DTS sound and built-in subtitles, a proper player like VLC is still the right tool.
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