Reply to comment

Thanks for your comments up there. I did eventually get it working by using cmd2exe from http://www.mailsend-online.com/ to turn a simple batch file into an exe, and put that in c:\windows, so that it would be found by google earth.

The batch file just contains the following two lines:

cd "C:\PROGRA~1\MOZILLA.ORG\SEAMON~1"
C:\PROGRA~1\MOZILLA.ORG\SEAMON~1\SEAMON~1.EXE -osint -url "%1"

and then once turned into SEAMON~1.EXE and put in %windir%, things just work again.

Apparently the quicktime player does a similar thing - it looks in the registry for the HTTP handler, and then strips any commandline options off and runs whatever is left. This causes all sorts of other issues.