I have been using this module with on Debian Etch with success, but on Debian Lenny (latest stable release as of February 2009), it's got problems:

It installs with force, but when using it from Mozilla::Mechanize it fails with memory fault. I have tried installing it both on an old upgraded server, and on a completely new, fresh installed server.

Here are some observations from the Gtk2-MozEmbed installation procedure:
Makefile.PL warns: Unrecognized argument in LIBS ignored: '-pthread'.
'make' warns about redefined constants: NS_HIDDEN, NS_IMPORT_ and NS_EXPORT_.
'make test' badly fails: t/GtkMozEmbed.t crashes with memory fault(segmentation fault).
I have tried replacing -pthread by -lpthread in the Makefile