For now, if we implement a devtools interface in a Tab, this tab can't open a toolbox for a remote target. It can only display a toolbox for itself. But it would be great for about:debugging (as well as it would have been handy for the App-manager) to be able to display a toolbox for a custom target. About:debugging could be using CustomHost to integrate a toolbox on its own, but it introduces docshell issues we had while using this in the App-manager. It would be easier if we could just use regular Bottom/Side/Window hosts, but with a custom remote target.

Still need a test. Also I'm not sure picking the topmost window is best? May be the callsite should give a tab or a document in order to be explicit?

I forgot about this bug and patch. This feature is now better described in bug 1348012.