John: I don't understand what you're trying to do. Are you the manager of Telegraph.co.uk? Checking the https site, you can see why Firefox complains:
www.telegraph.co.uk uses an invalid security certificate.
The certificate is only valid for the following names:
*.akamaihd.net, *.akamaihd-staging.net, *.akamaized-staging.net, *.akamaized.net, a248.e.akamai.net
Error code: SSL_ERROR_BAD_CERT_DOMAIN
Technically, you don't even need to buy a certificate from DreamHost: we offer the free ones from Let'sEncrypt that work as well... what you need to do is to force your site to redirect all calls from http to https (use .htaccess rewrite rules, for example). And as LakeRat suggests, you'll have to make sure that the whole page only includes content served via https in the "src=" arguments (tipically images and videos).
If you have issues with your website, put the exact information here or we won't be able to help you: be precise, give URL, error messages, what you tried as debugging, what you expected and what actually happened.