Torbutton should detect its old default Tor proxy settings as Tor-enabled mode
We had a user in #tor complain that after upgrading to Firefox 9 and Torbutton 1.4.5.1, Torbutton would route traffic through Tor even when disabled. He/she/it had had Torbutton 1.2.5 installed and in Tor-enabled mode before the upgrade, so Firefox was configured to use Polipo, and Torbutton 1.4.5.1 did not recognize that set of proxy settings as being ‘Tor’.