Hm, so the blank window did come up, then? Browser Switchboard doesn't bring up the blank window until after it detects that MicroB is open, and the above suggests it didn't, so I'm not sure why the window appears here. The failure to actually use the browser suggests that something's wrong with the connection between it and the browserd too -- lots of strange stuff going on here.
Because I have no idea how to eavesdrop on D-Bus traffic using the GLib API (the present code does the same thing that dbus-monitor does).