Given https://bugzilla.mozilla.org/show_bug.cgi?id=1797423#c22, it would be interesting to try turning off HTTP/3 and seeing if this problem goes a way...
Bug 1800088 Comment 3 Edit History
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Given https://bugzilla.mozilla.org/show_bug.cgi?id=1797423#c22, it would be interesting to try turning off HTTP/3 and seeing if this problem goes away...