User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:57.0) Gecko/20100101 Firefox/57.0 Build ID: 20170913220121 Steps to reproduce: After an update to Firefox Nightly, I simply launched the browser, and the issue has been present since then. I have the title bar disabled. I am running macOS 10.13 Beta (17A360a) on a MacBookPro11,3. Actual results: The title bar appears to be overlaid on top of the tab area. There is a distinct color shift between two sections of the title bar, and the page title is displayed in the top-center, where it overlaps with tabs. The top left and right corners appear to have squares removed from them. A screenshot is attached below. Expected results: The page title should be absent, and the colors should be unified. In short, it should look like it does in every other screenshot rather than the one attached below.

Tracking requested: critical UI issue