How do I manually add a Trusted Site?
I've tried Tools.Options but it's not obvious (to me anyhow) how to define a trusted web site.
Firefox does not use the same Trusted Site system that Internet Explorer uses. With Firefox you can specify general privacy and security settings and then add exceptions for certain sites.
In Firefox 6 and newer, you can also manage everything via the new about:permissions page if you wish to give it a try.