This impacts some content on the site, but not all. Trying to find a regression range has been tricky. The media.eme.mfcdm.origin-filter.enabled pref doesn't seem to be tied to this, I have this set to 0 in Nightly and can still reproduce.
Bug 1911283 Comment 24 Edit History
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This impacts some content on the site, but not all. Trying to find a regression range has been tricky. The media.eme.mfcdm.origin-filter.enabled pref doesn't seem to be tied to this in nightly. Alastor says this is another issue with experimental hevc support.