Works great however it would be great if it had a text field where I could enter the websites I don't want to be mangled by this add-on.

One site, one line.

Subdomains will have to be matched too, e.g.

domain.com should also match one.domain.com and two.domain.com

A "Save" button would be nice, so that Firefox wouldn't save the contents of this field on every key press.