Tooltip does not disappear when switching windows
I run Gnome 3.30.1 on Ubuntu 18.10.
I use "focus follows cursor" in Gnome settings.
I open Thunderbird 60.2.1, position the mouse over a message in the message list. Then a popup (describing the message) appears. I press Alt+Tab, then the Thunderbird window disappears hidden by another maximized window but the popup does not disappear.
The popup should disappear when switching windows.