I think this would fall under frames... There is a screenshot following this post that explains what's happening better than words. To reproduce: Go to http://www.sendthisnow.com/html/apology.html right click on the photograph of the missles. Then select view only this frame. The screenshot shows the result. Mozilla is loaded within Mozilla.

on linux there is no "view only this frame" menu-item in the context menu that appears when i right-click the image. Reporter: Which build ID are you seeing this with?

Sorry for the missing info... Occurs on Nightly win32-installer Build 2001050104

The large photograph is not an <img> but an <input type="image">. Mozilla is mistakenly displaying the context menu for frames when you right-click on it so we get the "View frame in new window", "View only this frame", etc. Since those items expect a frame object but don't get one, Moz is freaking out and opening navigator.xul in the window. By the way, when I pull up the context menu on that photo, I can't get rid of it by clicking elsewhere on the page.

I've verified that this is present in today's build. Handing to the contextual menu guru...

Not a frames problem. A context menu problem with <input type="image"> which is bug 77122. *** This bug has been marked as a duplicate of 77122 ***