Close "sources" window

[Sir Yuu]

I'd rather not have this popup on the window for the rest of time, so how do I close it?

 

[Suslik V]

To prevent dock panes from popping out you can try main menu Docks > Lock Docks.
Reset Docks menu entry will reset position of the dock panes to default (no matter were they locked or not).

By making checked/unchecked corresponding menu entries (main menu Docks > Sources , Docks > Scene Transitions etc) you can show/hide dock panels.