Mozilla is adding support in Firefox 4 for a new technology called HTTP Strict Transport Security that enables site operators to tell browsers to always request an HTTPS session on future visits. The technology, which is also known as ForceTLS, is currently an IETF draft specification and Mozilla officials say it should give users more confidence in HTTPS connections over time. Firefox 4 currently is in beta and is scheduled to be released by the end of the year. The inclusion of HSTS in Firefox is another step toward establishing a higher degree of trust in HTTPS.
Source: https://threatpost.com/firefox-4-include-http-strict-transport-security-support-082710/74393/