^CORRECTION: With Media Hint enabled in Firefox, it disables all proxy settings and reverts Firefox to what amounts to 'direct unencrypted mode', or something like that (not sure exactly).
I discovered this because my home page for all my browsers is www.tracemyip.org
which tells me immediately if the browser is running through a VPN or got accidentally switched back to 'no proxy' mode, as was the case with Media Hint, and told me exactly where my actual location is.
I reset the proxy to TOR Vidalia, closed Firefox, reopened it, and it was still set to 'no proxy' mode, and www.tracemyip.org
unerringly told me my actual exact location again.
Only when I disabled Media Hint and reset my proxy to TOR Vidalia, did Firefox again work through TOR Vidalia properly, and give me a random 'location' again as TOR VIdalia is supposed to do.