STR: 0. Set about:config devtools.inspector.flexboxHighlighter.enabled = true 1. Visit https://hg.mozilla.org/mozilla-central/raw-file/75a32b57132f8cba42779555662a057a0416a313/layout/reftests/w3c-css/submitted/flexbox/flexbox-align-self-baseline-horiz-001b.xhtml 2. Inspect the first flex container (the upper blue dotted area) and toggle the flex highlighter. ACTUAL RESULTS: The baseline-alignment line is drawn at the wrong spot. It looks like it's being drawn as a measurement inwards from the wrong edge of the flex container, or something.

This works correctly in the "a" version of this test, BTW -- that can be used as a "reference case" here. (Just edit the URL to end in "a.html" rather than "b.html")

Per bug 1468859 comment 2, this doesn't seem to be reproducible at the moment, but it might just be that we've turned off this piece of the UI until we start focusing on the alignment inspector (bug 1492055).