This is an extremely beneficial add-on to enhance your privacy and security. Currently, it works with Chrome, Mozilla Firefox, and Opera. It arose as a cooperative effort between the Tor Project and the Electronic Frontier Foundation.
HTTPS Everywhere guarantees you server authentication, data confidentiality, and data integrity. It activates the HTTPS features of the websites you visit, if those exist. Your browser will not even attempt an insecure connection, and this can prevent an attack called “SSL stripping.”
It does not hide the identities of the websites you go to. Nor does it somehow make those websites safe. It merely activates the HTTPS security features of the sites you browse if those are present. This can be a significant plus for your privacy and security. The Tor browser comes with HTTPS Everywhere by default.