The Toolkit Error Console looks like absolute crap on Windows 10 because of it partly specifing its own style assuming Windows Vista-style Aero. Because this is not PURELY a style issue but also a structural issue with its multiple toolboxes as fallout from making it capable of being in-content with
about:console it needs some changes to sort it out.
This is related partly to Issue #1793 but the changes warrent its own issue. This will NOT be done ahead of the
CLOSED TREE tomorrow as it requires enough lead time for 3rd party themes to account for it.