After resetting the config setting mentioned above to the default (true) value again, and restarting firefox, the same string and any others entered in the location bar correctly were sent to the search provider selected in my search bar.

The only other thing that might have affected this is that I had recently made a temporary change to the selected search provider. But this had been reset to google before the above described search was misdirected to the internet service provider.

those useless pages are normally served through your ISP on invalid DNS requests. another way to mitigate that would be to configure your system to use an alternative DNS server like the one google provides: https://developers.google.com/speed/public-dns

See also http://en.wikipedia.org/wiki/DNS_hijacking

I've set my DNS addresses to 8.8.8.8 and 8.8.4.4 (Google Public DNS)

The problem has not happened again, but stopped before I made the DNS change. Charter Communications seemed to allow a way to turn off the "service" that had ignored my browser/preferences, so that might have done it.... I appreciate the responses, doubt Charter will get another chance to hijack DNS again.

There is this page however not sure if it is cookie based or if once you opt out it will not matter what browser is used or if cookies are removed. http://search.charter.net/prefs.php

Yep, James, this is the page where I attempted to disable the Charter Communications "Web Helper."

      But on revisiting the page, I see that it is nevertheless "enabled."  (So I have "disabled" it again, and an immediate recheck shows it is "disabled."  Guessing it defaults back to "enabled" if/ when cookies are cleared, which is sometimes needed to avoid other unsolicited "help."

Hopefully using Google Public DNS will prevent Charter from "helping" me any more with my "website preferences"! Thanks again to all who have addressed this issue.