Did you click on the video with the right mouse button and select Play from the context menu?

The page there is completely empty. Plane white screen. Here is a screenshot https://imgur.com/a/FBvqme5 even if i right click it already says it is playing, cause it offers me an option of "Pause".

Other videos on same website are playing http://yapx.ru/viral/DjHOw however particularly long in height do not. Yet same videos work in Chrome, Opera and others.

And before you suggest, I do have an updated Firefox. I am an advanced pc user myself and 99% sure the problem is in Firefox itself.

Can you play a video directly?

• http://i.yapx.ru/DjHOz.mp4

You can open the YouTube test page to check support in Firefox for playing HTML5 media.

• https://www.youtube.com/html5

If you use extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) that can block (wanted) content (Adblock Plus, NoScript, Disconnect, Ghostery, Privacy Badger, uBlock Origin) always make sure such extensions do not block (wanted) content.

• make sure your extensions and filters are updated to the latest version
• https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems

Firefox shows the shield icon at the left end of the location/address bar in case Content Blocking is blocking content.

• click the shield icon for more detail and possibly disable the protection

You can check the Web Console about what content is blocked

• "3-bar" menu button or Tools -> Web Developer
• https://support.mozilla.org/en-US/kb/tracking-protection
• https://support.mozilla.org/en-US/kb/content-blocking

Yes, I can. It does play it directly, strangely. However, it does not play on page as I have shown on the screenshot.

No content is being blocked either. What you are suggesting would be correct, if all videos would not been playing, however as I said, only long in height do not, while others do.

Does the Web Console show any error messages about playing media files?

• https://developer.mozilla.org/en-US/Tools/Web_Console

Does the Network Monitor show that Firefox retrieves this file?

• https://developer.mozilla.org/en-US/Tools/Network_Monitor

Errors are:

"This site appears to use a scroll-linked positioning effect. This may not work well with asynchronous panning; see https://developer.mozilla.org/docs/Mozilla/Performance/ScrollLinkedEffects for further details and to join the discussion on related tools and features! DjQag uncaught exception: TagError: adsbygoogle.push() error: No slot size for availableWidth=0"

and in Network monitos it seems like it doesn't. At least i could not find DjQa4.mp4.

Does it work perfectly in your browser? I am using Firefox Developer Edition 66.0b14 (64-bit) on Windows 7

Here https://imgur.com/gallery/zPbTq1K is the same thing. The video plays only in Chrome, Opera and others.

That is this video:

• https://i.imgur.com/pXgYF0u.mp4

You can create a new profile to test if your current profile is causing the problem.

See "Creating a profile":

• https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles
• http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Profile_issues

If the new profile works then you can transfer files from a previously used profile to the new profile, but be cautious not to copy corrupted files to avoid carrying over problems.

• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox

Listen, you trying to point that my problem is locally. I do not think so, because its the same problem only in Mozilla browsers on two completely different computers.

bashmanov.o said

I have noticed that particularly long in height videos do not play in Firefox, but play in Chrome, Opera and other browsers. Here is the link for such video: http://yapx.ru/v/DjQag

Plays ok for me with FF 65.0.2 on that page (looping) and directly (a 10-second MP4 video). I don't know if it's FF-66-specific or something at your end.

What's your Content Blocking settings and what Extensions do you have?

~Pj