Comment 55 for bug 849624

I was using -url since osx LaunchServices uses this switch to start up ICS files, but it will have the same problem as noted in one of the TODO comments:

Regardless of windows,linux,mac, how do we know if the url passed (either without a switch or with -url) is one that calendar can read? The way the commandline interfaces work we need to do this synchronously, which means we can't just open the URL and find out.

In an ideal world, if the url is one that calendar can read, then i.e the .ics file that was doubleclicked on should be subscribed to, otherwise it can be left to thunderbird to decide how to open it.