I can reproduce the failure in Nightly as well (by visiting http://localhost:8000/css/css-backgrounds/border-image-width-006.xht while the WPT server is running)
Bug 1567639 Comment 10 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 the failure in Desktop Nightly as well (by visiting http://localhost:8000/css/css-backgrounds/border-image-width-006.xht while the WPT server is running for a desktop mozilla-central WPT run)