NoHTTP от Christian Moore

NoHTTP is a simple add-on that prevents insecure HTTP requests from being made by re-writing all HTTP requests as HTTPS. Sites that do not support HTTPS will fail to load, and sites that redirect from HTTPS to HTTP will result in a redirect loop.

After installing the add-on, click the shield icon to toggle HTTP to HTTPS redirection on or off. A blue shield indicates the add-on is ON and redirecting. A grey shield indicates the add-on is OFF and not redirecting.

If you encounter any sites that cannot be loaded over HTTPS, you must toggle NoHTTP OFF in order to load the page.