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I've been searching for an answer to this for weeks to no avail. It concerns YouTube videos "autoplay"ing on YouTube. Many have asked this question and most responses state to shut off Autoplay. These are two separate issues. AotuPlay means the next video on YouTube will advnace automatically requiring no user input. If Autoplay is off, streaming stops at the end of the video. The issue I am having is when I open a YouTube video to a new tab (but do not switch to that tab), the video WILL start playing as soon as that tab is in focus. This never used to happen and indeed, on two other computers with the settings and extensions all sync'ed, this doesn't happen, except for on this one computer. Today I found someone that posted the exact same problem 5 years ago and didn't get an answer. He seems to describe it well:

1. Okay, so before, when I loaded up 100+ Youtube videos, they stayed when switching tabs - no autoplay. Suddenly they decide to autoplay when switching tabs - note, I've not done anything to my settings or plugins. Fair enough, maybe you changed something (which you often do, without informing). So I check the options. It was on "Block audio", which obviously didn't work, so I tried "Block Audio and Video" - which WORKS, but now both the video is paused (which I want) AND the audio is set to mute (which I DON'T want) - so... what does it take to have Youtube wait for a click to start playing a video loaded in a background tab, but KEEP AUDIO ACTIVE, so I don't also have to unmute the damn video?

One person posted a possible solution: Maybe check this pref on the about:config page.

   media.block-autoplay-until-in-foreground 

This setting describes the issue kind of. If you have this set to false, the moment you send a link to a new tab, YouTube starts playing in the background. Setting it to false keeps the video paused until that tab is in focus. That is how mine has always been set. What I am looking for is a setting that would say something like: "block autoplay until play is pressed"

Thanks in advance and sorry for being so long-winded

Maybe after update, or i dont know why, but now. when youtube (or any other videoplayer) in fullscreen - taskbar menu is visible (Is on topscreen). In google chrome problem is not repeats. I'm using StartAllBack app for classic start menu, but till that day all was fine. I checked on two devices with firefox - the same problem (StartAllBack or windows version wasnt cahnged). Windows 11 24H2

Some videos on X don't play. They show the continuous circle loading. Copy that video link and load in private browser and it plays normally. How do I find out what is keeping them from playing in the normal browser. I tried disabling all extensions. No change. Any ideas I can try?

I´m currently working on some courses in Udemy and all of a sudden the videos are not loading, is not my internet connection I deactivated all the extension to see if it was the case but nothing seems to be working

Windows 11 Pro - Dell XPS8940 desktop - i9

Firefox will not play video from a website. If I save the video, it is a MP4 file. Windows Media Player and VLC will play the video file. But the browser shows the message: "No video with supported format and MIME type found."

Chrome and Edge will play this video correctly in their browsers. Firefox will not play the video on 3 different computers, and even when a different user account is involved (without Firefox sync).

The evidence seems to point at firefox. The website is a Wordpress site.

Is it possible that the website is the problem? If so, why do Edge and Chrome work?

I uninstalled Firefox (latest version) and reinstalled it. Not fixed.

My windows updates are current, as are Dell updates.

This is stumping me. I hope someone can help.

This is the link. I can't send animated images as the text is too small, so I'll describe it instead. It's so hard as a loyal fan, I'm crying.https://www.bilibili.com/bold text。There is a bug. Why does the Bilibili website not display the corresponding screen when I try to move to it? Speed playback cannot be used at all, and there’s also the issue of not being able to use fullscreen on Firefox. Are you forcing me to use another browser?

Hello people,

Please some help around the following issue, since a few days, Firefox will not play mp4 files directly in the browser. What it does when clicking to open an mp4 from the file server, it saves the file first and then opens a window to play it. Or it directly provides the save dialog window instead of playing it in the browser window directly.

Any ideas, appreciated. I have a lot of files to assess for my students, and this browser behavior makes it very tedious.

Greetings.

This issue came up in early April 2025.

Programs other than Firefox (e.g. Edge, Media Player) behave normally: when playing sound, if nothing is plugged into the 3.5 mm jack, the sound comes from the desktop's external speakers; and when an audio device (speakers or headphones) is plugged into the 3.5 mm jack, the sound instead comes from that device.

Where as Firefox will play using the internal speakers as expected, but when a device is plugged into the 3.5 mm jack, no sound signal goes to that device.

It seems then that the hardware is okay, and the problem must lie within Firefox, or within a Windows setting that is very specific to Firefox.

The sudden onset earlier this month may point to either a Firefox update, or (less likely) a Windows update.

Initially connects video playing to Headphones via Bluetooth then audio stops. Reloading doesn't help. But the same works perfectly on other browsers. Problem is with Firefox audio setting. The problem started only a week ago for firefox

MP4 Not loading:

I have uploaded a few MP4 animated images to our website, but they are not loading in the Firefox browser. It looks like they are getting corrupted. This issue only occurs in Firefox. I’ve also attached screenshots for reference. Can someone help me understand why they are loading like this?