The app does not work on Leopard - either with Safari or Firefox. It seemingly gets installed okay (although you won't find any traces of it in the system with Spotlight - only when you launch Safari or other browser and look into Service), but the command just doesn't work: in Safari's Service it shows in black, but a click on 'Print Selection' gives you nothing except freezing the browser (a repeated click outside the Service window revives it, however). In Firefox's Service, it's displayed as inactive at all - grey color.

I also wonder about Apple's sort of arrogance - having in mind the bewilderment of so many Mac users, especially Windows converts: The app is just 168 kB - they could've long assigned an experienced programmer with that kind of a 3-4 hors job to solve the problem once for ever, couldn't they?