Could you try quitting and restarting Firefox and see whether that makes a difference? I noticed when switching user agents with the Phony extension that I had to do that (last checked a few versions ago).

Bingo! I had skipped a few versions of firefox, and on the last one I used phoney didn't require a restart.

I actually changed the max version in the phony xpi and installed. Under the hood all it is doing is switching general.useragent.override, and I could see it making those changes. Phony says it doesn't work past r22. It appears phony is working fine, it's firefox that's broken.

Thanks for the reply!