Two more points:
a) We should write "black window" instead of "black screen". Only the Firefox's window is black. As you can see on the screenshot.
b) After I have a black window (whatever the way I obtain it), typing Ctrl-W closes the window and Firefox menu icon doesn't have it's orange bullet nearby anymore. Then, clicking again on the Firefox's menu icon opens Firefox's window normally (no black window) EXCEPT that I lose every tabs opened in the last session (and yes, of course, I have properly configured the fact that I want to save the tabs between two sessions).
Two more points:
a) We should write "black window" instead of "black screen". Only the Firefox's window is black. As you can see on the screenshot.
b) After I have a black window (whatever the way I obtain it), typing Ctrl-W closes the window and Firefox menu icon doesn't have it's orange bullet nearby anymore. Then, clicking again on the Firefox's menu icon opens Firefox's window normally (no black window) EXCEPT that I lose every tabs opened in the last session (and yes, of course, I have properly configured the fact that I want to save the tabs between two sessions).
Hope that helps!