I just installed and started to use 18.04 (finally! I got a computer that supports it especially...)
When I open certain windows, such as Thunderbird and Virtualbox, they at times open child windows and those appear on top of the parent window completely obstructing it. So... I'd like to move the child window out of the way and ... that means the parent window along. In other words, the window in the background remains obstructed. Who thought of this beautiful feature?! (Yes. Sarcasm.)
I'm wondering whether this is something I can turn off. Maybe a parameter in the gconf-editor?
Oh! I actually found it. It's in the Gnome Tweaks under Windows and the very first option is called Attach Modal Dialogs. As we can see here, by default it's turned ON. Click on that button so it says OFF. Now you do not get a grayed out window and when you move the modal dialog, it doesn't move the parent along. Much better!