The API to xulrunner changed in 1.9.1, I filed the bug upstream http://bugzilla.gnome.org/show_bug.cgi?id=565669 and they have fixed in SVN trunk, so to fix the broken deps, epiphany probably needs to be updated to an SVN snapshot.
As noted here: http://bugzilla.gnome.org/show_bug.cgi?id=565669#c2 the epiphany developer can't test that the fix actually works (he doesn't have access to xulrunner 1.9.1) so it would be good if the SVN snapshot and/or point release (hopefully they will make one) could be tested to see if it actually works.
I have managed to build Rawhide epiphany http://koji.fedoraproject.org/koji/taskinfo?taskID=1052223