Created attachment 1507427 [details]
Firefox with black area in overview
Description of problem: After starting Firefox the maximized window is not restored but leaves black area around it.
Version-Release number of selected component (if applicable): all newer versions, this is not a new issue; but possibly Wayland-only; also happened in F28 IIRC
Steps to Reproduce:
0. Firefox must be closed from a maximized state.
1. (Preferably after a computer restart) start Firefox.
The window is shown completely functional and "properly" in the top left corner
You can work around it by just dragging the window from the top once (then it is really de-maximized and you have it in your hand) and snap it back to the top, which maximizes it properly.
In the attached screenshot you can see it like that. I have cropped the top to hide my bookmarks and things like that, but they are all shown as expected. The screenshot is also made from the GNOME applications overview, as you can see from the blue border around the window, which I am hovering over.
Thus you can see it is really Firefox that has this fault, and unless you change the window size/maximization state in any way, it also stays like this.
How reproducible: Sometimes. Not always.
It's already tracked at upstream - https://bugzilla.mozilla.org/show_bug.cgi?id=1489463