Firefox takes 5 to 10 minutes to start playing and is jittery

[Marco2G 4]

Hi

I noticed over Christmas that a DVD rip of Muppet Christmas Carol took literal minutes to start playback and then the pan over the houses at the beginning was jittery.

Now my wife noticed she sees the same thing in a Chosen Bluray rip. Well, the playing delay.

Firefox takes anywhere from a few minutes to what feels like an eternity to start playing.

So I tried many things with that Muppet rip. ChatGPT had ideas about the file possibly having garbage in it or because it's PAL, wrong color coding and so forth. Nothing helped. In the end, I tried Brave and all issues were gone.

I have two kubuntu machines on which the issue was noticed and one Windows 10. So it would have to be an inherent issue with the Firefox engine, I think.

Anyone know what this might be? Can it be fixed or is it time to give up on Firefox entirely?

[Neminem 1516]

Is it transcoding ?

What video codec , audio codec etc.

 

[Marco2G 4]

Is it relevant? Transcoding happens server-side and would presumably happen equally for both browsers?

[Neminem 1516]

Not if one browser supports the codec and the other does not.

For more info is relevant to better guide you

[Marco2G 4]

Okay I'm testing.

Muppet Christmas Carol. Not a single ffmpeg log file is generated for any of this:

My machine is kubuntu with a 2.5Gb/s connection.
My internet is handled via 5G modem. The emby service is behind an NPM.

Firefox connecting internally took about a minute to start playing. 
Firefox connecting via Internet took several minutes.
Brave immediately started internally AND via internet.

I notice I have no idea how to find codec information in Emby. VLC says this:
Codec: H264 - MPEG-4 AVC (part 10) (avc1)

Video resolution: 720x552

Buffer dimensions: 720x560

Frame rate: 25

Color primaries: ITU-R BT.601 (625 lines, 50 Hz)

Color transfer function: ITU-R BT.470 BG

Color space: ITU-R BT.601 Range

Chroma location: Left

 

Audio:

Codec: MPEG AAC Audio (mp4a)

Does this help?

[Neminem 1516]

2 hours ago, Marco2G said:

Firefox connecting internally took about a minute to start playing. 
Firefox connecting via Internet took several minutes

Those kind of files should load fast, as in Brave.

As you have pointed to its a firefox issue, but I don't have that issue with this version of firefox.

Have you tried cleared cache in browser?

Are you on firefox beta?

Have you tried loading firefox with out plugins?

 

[Happy2Play 9780]

Need server log for specific example as it sounds like client is Downloading the file.

[Luke 42077]

Quote

Anyone know what this might be? Can it be fixed or is it time to give up on Firefox entirely?

Hi, first we need to learn more about the cause:

Let's look at an example. Please attach the information requested in how to report a media playback issue. Thanks!

 

[Marco2G 4]

embyserver.txt
Here ya go. I'd look at timestamp 20:06 and forward.

Just now the stream started almost immediately in firefox connecting internally from my machine. From 20:06 onward it's a connection from the mediacenter, still connecting internally. THAT took longer again.

It seems the delay is fluctuating and the problem thus intermittent.

My firefox version is 146.0

[Luke 42077]

Firefox's direct play mkv support is brand new and my guess is that it's just not perfected yet.

[Marco2G 4]

What did we use before this brand new 'direct play mkv support' and how do I go back to that?

[Luke 42077]

It would get transcoded by Emby Server. There currently is no way to force that so I would suggest playing with Edge or Chrome.

Note, we did not change anything, but firefox is now reporting that it supports mkv so the web app is trying to direct play them.

[Marco2G 4]

I understand that but I think a 'force transcoding' option would be a good idea to have in any case.

 

Unfortunately, we don't live in a time where you can just assume "Well, hurr durr, a Corporation like Mozilla, Microsoft or Google surely wouldn't release an obviously untested, shitty product!"

It's the same thing as with an option to change how much Emby buffers per default. I know in the US they still fleece people for every megabyte they transmit but in the Old World there are flatrates and I'd rather be able to buffer five minutes of a show or movie at a time if I know I am travelling through sketchy reception.
Edit: I just realised it doesn't even matter how much Emby buffers... If I want to watch the whole thing it'll have to transmit the whole thing... So why do we buffer like it's Youtube anyway?

 

Edited January 9 by Marco2G

[Luke 42077]

I agree, however my advice was based on what you can do right now.

[Luke 42077]

Quote

So why do we buffer like it's Youtube anyway?

In the web app Emby doesn’t buffer. It’s all handled by the browser video player.

[Marco2G 4]

2 minutes ago, Luke said:

I agree, however my advice was based on what you can do right now.

So basically that is a yes to the question in my first post, got it.

 

 

2 minutes ago, Luke said:

In the web app Emby doesn’t buffer. It’s all handled by the browser video player.

On the go I use the Android app. The web app is only used at home. 

[Luke 42077]

Normally a video player will look at the headers in the beginning of the file which gives it information about the rest of the file. 
 

My guess is the headers in your mkv are either incomplete or formatted in a way that Firefox isn’t handling and therefore it needs to have the whole file before it can start playing.

[Marco2G 4]

Now that's interesting... but in that case I'd love to have a way to check for that and fix it in my source media.

Can the mkv quality be checked with ffmpeg or a similar tool?

[Luke 42077]

I’m not sure but one thing to try is remuxing it to a new mkv using mkvtoolnix

[Marco2G 4]

I have remuxed using ffmpeg but that didn't help. 

Just to make one thing clear, this file and others that show issues aren't some torrents off the net. I have ripped them myself using MakeMKV and worked them over with Handbrake. Now I grant you I could well have used the wrong settings there.

But I also tried remuxing with ffmpeg. No change. But I'll see about trying with mkvtoolnix

 

[Marco2G 4]

Okay, not sure how to use the tool. The output file was generated inside a few seconds... don't know if it really worked... but it sure makes no difference to the emby web app in Firefox.

[Jefemy 3]

The recently released Firefox MKV support doesn't allow for partial retrieval of the video content it seems. You can disable it by going to about:config and changing media.mkv.enabled to false.

[Marco2G 4]

That indeed solves all problems. Thanks.

[SLMK 19]

On 1/10/2026 at 8:17 AM, Luke said:

I agree, however my advice was based on what you can do right now.

Please add force transcode as an option, ideally both server side per account, and client side options.

Playback and transcoding work well most of the time, but Ive run into quite a few edge cases over the years that this would have solved.

On 1/20/2026 at 10:08 AM, Jefemy said:

The recently released Firefox MKV support doesn't allow for partial retrieval of the video content it seems. You can disable it by going to about:config and changing media.mkv.enabled to false.

Worked for me as well, thanks.

[yocker 1247]

5 hours ago, SLMK said:

Please add force transcode as an option, ideally both server side per account, and client side options.

Playback and transcoding work well most of the time, but Ive run into quite a few edge cases over the years that this would have solved.

Worked for me as well, thanks.

The user can go into settings and set a lower quality.
Easy way of getting it to transcode.