Created attachment 644961 [details]
I tried using the "pref set" command in a recent nightly ("Mozilla/5.0 (Macintosh; Intel Mac OS X 10.7; rv:17.0) Gecko/17.0 Firefox/17.0") and received an error and HTML in the GCLI.
(see attached screen)
and now I'm unable to reproduce this attempting "pref set social.enabled true".
I also can't reproduce this now. I'm going to close it, and we can re-open if we find it again.