... so that KML files (when clicked in the browser, e.g. in a Google search result) open in Google Maps, not say Google Earth?

http://maps.google.com/support/bin/answer.py?hl=en&answer=41136

http://www.ogleearth.com/2006/04/google_maps_2_g.html
.

Just to clarify: I know how to do this manually, but I'm looking into a way to configure Firefox to open "http: //foobar.com/something.kml" using "http: //maps.google.com/?q=http: //foobar.com/something.kml", which means it would result in it being overlayed on Google Maps.

http://rafb.net/p/mJTcKy17.html

Cool, did you just program that?