I had this problem also. I fixed it by changing my browser preferences in "Preferred Applications" from "Custom"(/usr/bin/firefox "%s") to "Firefox"(firefox %s).
-- webbrowser incorrectly handles quoted arguments for GNOME browser configuration https://launchpad.net/bugs/83974 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
