Here is a video showing the issue:

https://youtu.be/zUplVvsgf_Q

A link would be helpful. Is it just that 1 video? I have no issue on the site with any video using my distro or Mozilla version of Firefox.

Try downloading Firefox from Mozilla. Download, unzip, and run firefox-bin from the folder and see if you have the same issue. https://www.mozilla.org/en-US/firefox/all/#product-desktop-release

Are in using Wayland or X11?

Operating System: openSUSE Tumbleweed 20230318 KDE Plasma Version: 5.27.3 KDE Frameworks Version: 5.104.0 Qt Version: 5.15.8 Kernel Version: 6.2.6-1-default (64-bit) Graphics Platform: X11 Processors: 8 × Intel® Xeon® CPU E3-1535M v6 @ 3.10GHz Memory: 62.2 GiB of RAM Graphics Processor: Mesa Intel® HD Graphics P630 Product Name: HP ZBook 17 G4

I am using X11. But I even experience the problem using Mozilla on Windows 10. And I have a 1Gb fiber connection to the internet. In order to experience it, you go to the url I provided, then click to open one of the articles. The video embedded in the article will flash wildly like that.

Do you have the same issues on other sites? Do you have ffmpegs installed on Linux? I cannot replicate the issue in Linux, Win 11, nor Mac.

Did you try Firefox from Mozilla?

I did just now. It works perfectly. The one with the problem was downloaded from Ubuntu software servers. I will re-check Win 10 again, but will do the same thing if I notice the issue. Thank you for the guidance!!