You're welcome. I came across your post when looking for something else and realized how frustrating it is. We were hit by that a few months ago and had to explain to my users how to disable it.
Your post prompted me to finally file that bug with mozilla. There's no way Kerberos authentication...
In doing these steps, be patient and hit escape any time that Authoxy message comes up... It will happen many times...
1)Launch Firefox.
2) type in about:config to the address bar.
3) Agree to "voiding warranty" message (if it shows up.. depends on version)
4) Type in "auth" to the Filter...