User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:63.0) Gecko/20100101 Firefox/63.0 Build ID: 20180709100247 Steps to reproduce: Put Firefox in fullscreen mode on macOS. Move the cursor to the very top so that the macOS menu bar will appear. Tested with macOS 10.13.5 and Firefox 61.0.1, but same effect with earlier versions Actual results: The macOS menu bar and the title bar of firefox appear. They will be put on top of the firefox tabbar and the shadow of the titlebar will also make most of the firefox address-bar unclickable. Expected results: The tabs and the addressbar should scroll down while the macOS menu bar is visible. Both Chrome and Safari scroll the tab+address bar down when the menu bar is visible. It is really annoying when a user wants to switch tabs but when he moves the cursor a little bit to high up, the tab will be covered with the macOS menu bar. The user has to move the cursor back down and slowly up again to finally switch the tab.

User Agent:   Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:63.0) Gecko/20100101 Firefox/63.0 Build ID: 20180711100118 I manage to reproduce this issue on Mac 10.13 with Firefox Nightly 63.0a1 (2018-07-11) (64-bit).