with the pref enabled users would be prompted whenever mozilla decided
that it wanted to use another dns entry:
--
Failed to connect to http://www.evil.com
IP Address: 66.66.66.66
DNS records for www.evil.com indicate the following addresses:
.____________________________________.
|[66.66.66.66=-=localhost.localnet]|^|
| 10.0.0.1    - jackpot13.localnet | |
| 10.0.0.2    - localhost.localnet | |
| 192.168.0.1 - neighbor.localarea | |
|__________________________________|v|

Click connect to allow mozilla to connect to the selected address(es).

/!\ This site may be trying to use your browser to access servers that it
would otherwise be unable to access. If you suspect that is the case, you
should select cancel or block host and contact your administrator or the
site administrator.

< Connect > < Cancel > < Block Host >
--
Clicking Connect would add the selected ip address to the dns cache for
the session. I'm not sure that reverse listings for ip addresses would be
helpful, the art above includes them, but my original art didn't. In this
case reverse dns for 66.66.66.66 got lucky and matched one of its victims
just to show how potentially useless and misleading such a field could be.

[==] is just your normal selection mask.