User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:125.0) Gecko/20100101 Firefox/125.0

Steps to reproduce:

If I don’t enable the popular uBlock Origin extension, which is necessary to block ads, then videos on YouTube in Firefox stop playing normally.

1. Disable the uBlock Origin extension;
2. Open any video on YouTube;
3. Manually set the highest possible quality by clicking on the gear in the lower right corner of the video window;
4. I click anywhere on the timeline, after which the video loads a little, and then stops loading further (an endlessly rotating ring appears in the center of the video window). See screenshot: https://i.imgur.com/bN3M9Q4.png
   I'm using a Mac mini with an M1 chip. Just the other day I reinstalled the operating system completely, completely formatting the built-in SSD drive. My macOS version is the latest - 14.4.1 (23E224). Firefox itself also installed completely. There are no problems with this in Chrome and Safari! I tried a bunch of different options and settings, including disabling hardware acceleration. Nothing helps! The firewall in the operating system is disabled. Please tell me what should I do next?

I tested this in the latest dev version of Firefox (126.0b5) but the result is the same.

Let me clarify once again that Firefox and macOS are pristine, installed from scratch! Therefore, resetting the settings to default, clearing the cache, etc. makes no sense.

The Bugbug bot thinks this bug should belong to the 'Core::Audio/Video: Playback' component, and is moving the bug to that component. Please correct in case you think the bot is wrong.

Although this problem occurs with uBlock Origin enabled. I just clicked anywhere in the timeline and the video froze. Screenshot: https://i.imgur.com/ctHJunj.png Even after a few minutes, playback does not start. This problem is just driving me crazy! Please fix it as soon as possible 🙏

Maybe you need to enable or change some settings on the about:config page or in Firefox settings? Maybe you need to change some parameters in the macOS system settings? Maybe you need to change some parameters in the router settings? 🤔 But why then does everything work without problems out of the box in Chrome and Safari? This is definitely some kind of strange bug that greatly ruins the user experience! I just can't watch YouTube properly in Firefox 😕 Because of this problem, I even installed macOS and Firefox completely from scratch, but this does not help 😢

Can anyone confirm the presence of this nasty bug?

I cannot confirm it. On my M1 Macbook Pro, with Firefox 125.0.3 on a fresh profile with no add-ons, I can drag the video playback head to any position and the video plays correctly from that position.

Try clicking LMB several times in a random place on the timeline. After each click, wait at least a few seconds to make sure the video loads further.

Try clicking LMB several times in a random place on the timeline. After each click, wait at least a few seconds to make sure the video loads further.

If you still have no problems after this, then write what I should do so that you can diagnose this problem 🤔

I've clicked 100 times now, no problems.

Can you capture a profile with the Media preset, upload it and link it here?
https://firefox-source-docs.mozilla.org/performance/reporting_a_performance_problem.html

I stopped profile recording just when the video on YouTube stopped loading after another LMB click in an arbitrary place in the timeline: https://share.firefox.dev/4bdr72W

I have now checked for this bug in Safari 17.4.1, Safari Technology Preview Release 194 and Chrome 124.0.6367.202. Everything is fine! 👌 No browser other than Firefox has this annoying problem. Please tell me what are my next steps to fix this issue in Firefox?

(In reply to 5silentrain from comment #12)

I stopped profile recording just when the video on YouTube stopped loading after another LMB click in an arbitrary place in the timeline: https://share.firefox.dev/4bdr72W

Thanks! Can you get another one where, once you notice that it's stuck, you let it show loading spinner for 20 seconds before you capture the profile?

The network chart of the last 20 seconds of your profile shows that requests are served quite consistently: https://share.firefox.dev/3QFCFnD

Please be patient, it can take a bit of back and forth to diagnose issues like this. If we knew what caused it we'd tell you.

Maybe I should select "Network" rather than "Media"? 🤔 Because it looks more like some kind of issue with the network, rather than with the media.

Both may be useful. I'd start with Media but you might as well also get a separate profile with Network while you're at it.

I started playing this video and already at the 5th second it just froze: https://www.youtube.com/watch?v=rIYBi97ZKF8 I didn't even have time to do anything! LOL!!! 🤣 After the video froze at the fifth second, I waited 20 seconds, as you asked, and only then pressed Ctrl + Shift + 1. This is for "Media": https://share.firefox.dev/4byw71Q

This is for "Network": https://share.firefox.dev/3QHgZax

The first profile shows one succeeding request but then no further network request is made and I don't see a transition from "video playing" to "video not playing". I think I need another profile (Media preset) which includes the video playing correctly before it gets into the bad state.

The second profile just shows YouTube spinning and no evidence that YouTube is making another attempt to fetch more data.

Played this video again: https://www.youtube.com/watch?v=rIYBi97ZKF8 Started recording the profile before pressing play. That is, the profile should capture the normal state before the video froze again literally at the beginning of playback.

https://share.firefox.dev/4bc1FuS

Great, the last profile is exactly the type of profile we need here.

One thing that stood out to me in this profile is that the last long network request before the forever-spinner has a preconnect associated with it. I wonder if that's true every time.

Can you capture two more profiles of the same thing? Then we can check if the failures have anything in common.

Okay, here it is:
https://share.firefox.dev/4anz7gQ
https://share.firefox.dev/4adQH6H

Hmm, mixed results so far.

All profiles show long-running network requests for the video data, where some requests cause new frames being fed to the video, and other requests don't cause any frames to be sent to the video.
I'm going to call the profile from comment 20 profile A, and the ones from comment 22 profile B and C.

In profile A and B, the long-running requests without frames are associated with a preconnect:
https://share.firefox.dev/3yekJdj
https://share.firefox.dev/3WDufAY

In profile C, the long-running requests without frames did not have a preconnect:
https://share.firefox.dev/3wrCuFx

John, do you have any further insights based on these profiles?

Guys, please also note that with the ad blocker enabled (uBlock Origin), these problems occur to me much less often, so before I didn’t pay much attention to them. At the same time, in Chrome and Safari, even with the ad blocker turned off, I have NEVER managed to encounter this strange problem. That is, there are suspicions that the problem is in Firefox.

Changing the User Agent does not help. I specifically installed an extension that changes the User Agent. I chose Chrome as the User Agent. Firefox still doesn't load YouTube videos properly 😢

I tested it on a regular computer running Windows 10 Home (this is an Intel nettop that my brother uses). Everything is the same — video playback on YouTube in Firefox constantly freezes. In this video, for example, the video constantly freezes at the very beginning, at the 5th second: https://www.youtube.com/watch?v=rIYBi97ZKF8

I think I’ll have to switch to Chrome or Safari, because I watch YouTube regularly.

In this video, for example, the video constantly freezes at the very beginning, at the 5th second: https://www.youtube.com/watch?v=rIYBi97ZKF8

Screenshot: https://i.imgur.com/Nsy814Q.png

Alastor, might this issue be the same as bug 1878510?

By the way, it’s very similar to my case! 😲

I'm glad that I'm not the only one who has difficulty playing YouTube videos in Firefox. Apparently the problem, after all, is in Firefox itself, and not in my computer, router and/or Internet provider 🤔 After all, Chrome and Safari do not have such problems under the same conditions.

@alwu
If you have a free minute, please take a look at this bug report, which is related to the small cache size that Firefox stores for YouTube: https://bugzilla.mozilla.org/show_bug.cgi?id=1840309#c5

There are no problems with this in Chrome and Safari.