HTTPS-First

When browsing with HTTPS-First, Firefox will always try to connect to websites using HTTPS first, to make sure that your connection to the website is encrypted and secure. So you have peace of mind that no one can snoop on the content of the pages you visit or hack into your connection to a website to steal your passwords, credit card information or other personal information. Most websites already support HTTPS; some support both HTTP and HTTPS. With HTTPS-First Firefox will try to make sure that you have a more secure connection whenever it is available. HTTPS-First is enabled by default in Firefox 136 and above.

Secure Site not available

Some websites only support HTTP and the connection cannot be upgraded. If an HTTPS version of a site is not available, the site will load but through the less secure HTTP protocol. In some cases websites seem to support HTTPS but serve different content from the HTTP version or behave different in other ways. To avoid upgrade attempts users can enter an address in the address bar with an explicit http:// scheme. Permanent exceptions added in the [HTTPS-Only Mode section] in the settings will also prevent upgrades.

What is the difference between HTTP and HTTPS?

HTTP stands for Hypertext Transfer Protocol and is the foundational protocol for the web and encodes basic interactions between browsers and web servers. The problem with the regular HTTP protocol is that the data transferring from server to browser is not encrypted, meaning data can be viewed, stolen, or altered. The HTTPS protocol fixes this by using an encrypted connection protects sensitive information. It uses digital signatures with public certificate, to ensure that the encrypted connection is established to the right end-point.