There is an object on the next line whose mime type is not known. It should say so. If nothing appears below this paragraph saying that the image could not be fetched, then there is a bug:

This test worked! The mime type was not recognised! Yay!

Something should be in the gap above. There should be three paragraphs on this page! (Note. A crash may occur if you select the object element, that has already been filed as bug 15018.)