Open a web page where there's some link with target="_blank" for some data which
is not viewable internally in Galeon but requires some external viewer. For
example, pdf with no pdf plugin installed. Click the link. Galeon will open a
new Galeon window, ask to open the file, and then pops up another window, this
time the external viewer. The empty Galeon window will remain haunting the desktop.

Galeon should defer opening a new window until it knows whether the arriving
data is displayable internally or not. Failing that, it should at least clean up
excess windows as soon as it figures it out.