User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Firefox/45.0 Build ID: 20170419042421 Steps to reproduce: Open a moz-extension: page with windows.create() and type "detached_panel". Actual results: It shows a blank page, but the content is loaded. When right clicking to open a context menu, the content appears normally. Expected results: It should show the page normally from the start, as with Firefox 52. Type "popup" and "panel" do the same as "detached_panel"; type "normal" shows correctly. Loading an http: page works as expected.