URL: https://binary-opacity-grid.github.io/

Browser / Version: Firefox 123.0
Operating System: Windows 10
Tested Another Browser: Yes Edge

Problem type: Video or audio doesn't play
Description: There is no video
Steps to Reproduce:

1. reproduce: Load site, get error displayed. No video with supported format and MIME type found. Issue is embedded H264 MP4 video.
2. Updated Firefox v123
3. reproducable, works in Edge browser

Example of said embed:

View the screenshot

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