plugin prompt is parented to wrong window

While reviewing older bug comments (see ticket:18937#comment:35), brade and I reproduced a problem: the confirm prompt for disabling plugins is attached to a dialog which is in the process of closing rather than being attached to a browser window. On OSX, this results in the dialog having a black background before closing (closing the prompt without user interaction). On Windows the prompt never appears.

Steps to reproduce: Open Torbutton's Privacy and Security Settings dialog Uncheck "Disable browser plugins" Click OK

We will post a patch in a few minutes.