Dragging Private Tabs to non-private window malfunctions

[xpev]

If you create a private Tab and use Drag & Drop to move so it would create a new Firefox Window a new window gets created but the Tab itself becomes useless. The URL is gone, you cannot close the tab and you cannot load a new URL. The new window itself is fine and new tabs (even private) can be created.

If you Drag & Drop tabs from a private window it does work normally.

[xpev]

I played a bit with that and found the following: If you move the private tab to a non-private windows the explained error happens. White window, tab unusable and unclosable. I even tried a fresh Firefox Profile, it still happens.
Before dragging: window1
Afterwards: window2

If you drag the private tab out of a non-private window into a private one it works as intended, the other way around also produces the error.

[Infocatcher]

Also see #237 (comment) and https://bugzilla.mozilla.org/show_bug.cgi?id=1279094 (for e10s, but looks like something related).

And for now works better with enabled e10s.
Also broken even without Private Tab, this caused only by following thing:

gBrowser.selectedBrowser.docShell
	.QueryInterface(Components.interfaces.nsILoadContext)
	.usePrivateBrowsing = true;

(that used inside Private Tab to toggle built-in private mode)