User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.9; rv:28.0) Gecko/20100101 Firefox/28.0 (Beta/Release) Build ID: 20140314220517 Steps to reproduce: Mac OS X Version: 10.9.2 - Open Firefox in fullscreen mode - open a website in a tab (2 tabs are now open in 1 fullscreenwindow) - drag one tab from the Tabbar to the bottom and release the mouse - a new window with the tab is created but with a black bar on top Actual results: New window will have a black bar above in fullscreenmode Expected results: no black bar should appear

m.summen, do you happen to use an external monitor? (bug 910144 and bug 931826). There is also bug 740923 (which was fixed for over a year ago).

Its exactly like the bug 740923.

Hi reporter, Using the latest Firefox release (43.0.4) and latest Nightly (46.0a1) but I did not encounter the issue described. Also, considering your latest comment, I will mark this issue as RESOLVED - DUPLICATE. If you still encounter this issue feel free to reopen it. Thanks, Cosmin.