Comment 8 for bug 250769

Created attachment 324752
move ws_info set up from nsObjectFrame::CallSetWindow() to nsPluginInstanceOwner::CreateWidget()

This is one way to solve the problem.
Perhaps another is to set up in nsObjectFrame::FixupWindow, or perhaps both
nsObjectFrame::Instantiate methods (or neither) should do CallSetWindow();

The build here has this patch and attachment 324576, for those who would like something that works:

https://build.mozilla.org/tryserver-builds/2008-06-11_23:<email address hidden>/

(I'll see if I can work out why the Instantiate methods differ.)