Version: 61.0a1 Build ID: 20180327120140 Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:61.0) Gecko/20100101 Firefox/61.0 Steps: 1. Open browser 2. Open Devtools and hover mouse over different tabs (contrast set to normal) 3. Change display settings contrast to a higher level than normal and hover over the tabs again Expected result: In each case a grey background should be shown, not just the grey overline. Actual result: When a user has the contrast setting set to higher than normal on macOS, in the Devtools menu the tab header grey background is not visible when hovering with the mouse, only the grey overline is visible.