Automator: action/service on right click on an url
Seems like "Service receives selected URLs" only works with Internet actions. Fortunately you can use the "Get Specified URLs" Internet action to relay the service input to your "Run Shell Script" action. 

For example, I used the following automator service to open a selected link in a non-default browser. In my case Firefox but you can use Chrome or another browser.



Remove any address from the "Get Specified URLs" action so that the list is blank as in the screenshot above. Don't forget to "Pass input: as arguments" In the "Run Shell Script" action if you're using the "$@" notation.