Well, I can verify that the site seems to work correctly. I don't use the extension to which you refer, but if it also works correctly for you with the extension disabled, it would certainly suggest the problem is the extension...
As for the address bar showing lock icons and not showing the http:// and https:// parts of the address...my guess would be that most people don't use them when typing in addresses adn they don't actually mean anything to the vast majority of people. Locks, however, are instantly recognizable as a security device. And, according to the relevant Safari Help Page:
"When you see a lock icon near the left end of the address and search field, you know that you are visiting an encrypted website. The website uses the HTTPS protocol and has a digital identity certificate. Information is encrypted to keep it private as it’s sent to or from the website.
The lock icon is inside the Security button, which can be gray or green.
A gray Security button means the website has a standard certificate.
A green Security button means the website has an Extended Validation (EV) certificate, which requires more extensive identity verification than a standard certificate. A green Security button shows the name of the EV certificate owner.
You can view the contents of the website’s certificate by clicking the Security button."
