I can reproduce this bug on both Windows 10 and macOS 10.15. Nika says she can't reproduce on Linux.
Bug 1620341 Comment 2 Edit History
Note: The actual edited comment in the bug view page will always show the original commenter’s name and original timestamp.
I can reproduce this bug on both Windows 10 (closing the full screen YouTube tab with Ctrl+W) and macOS 10.15 (closing with Cmd+W). Nika says she can't reproduce on Linux.