I'm using the Firefox add-on version 1.7.8, with the default URL Components settings (subdomains not enabled), and it uses "bbc.co.uk" as the domain for "www.bbc.co.uk" and "evil.co.uk" as the domain for "evil.co.uk", so the problem you described doesn't exist.
Maybe this was a problem in an earlier version and it's been fixed?
Maybe this was a problem in an earlier version and it's been fixed?