When editing a bug, it is possible to link it to other bug tracking systems and installations in case it is related to these. [1] While launchpad.net is allowed, code.google.com seems to be prohibited. The domain code.google.com hosts some Firefox extensions (including Firebug) which we may want to link to their issues from bmo, and allowing this will also allow linking to Chromium bugs from Firefox equivalents. [1] https://bugzilla.mozilla.org/page.cgi?id=fields.html#see_also