That's a quite old area of the code. You would be best served by just trying to bisect it further down the the individual patch. I can't really predict what would be causing that that far back.
Bug 1730423 Comment 63 Edit History
Note: The actual edited comment in the bug view page will always show the original commenter’s name and original timestamp.
That's a quite old area of the code. You would be best served by just trying to bisect it further down to the individual patch. I can't really predict what would be causing that that far back.