Thanks for the bug report!
The reason this failed on Roberts machine is because he has disabled firefox somehow, and xdg-open doesn't work. If xdg-open fails, it would be good to show an error message to the user explaining what we tried to do, and saying that xdg-open didn't work. I don't know that we'll be able to let users work around the problem, they will need to fix xdg-open, but giving an error message is better than silent failure.
Thanks for the bug report!
The reason this failed on Roberts machine is because he has disabled firefox somehow, and xdg-open doesn't work. If xdg-open fails, it would be good to show an error message to the user explaining what we tried to do, and saying that xdg-open didn't work. I don't know that we'll be able to let users work around the problem, they will need to fix xdg-open, but giving an error message is better than silent failure.