Mozilla introduced the optional HTTPS-only mode in the latest version of Firefox 76 Nightly, which only allows connections to HTTPS sites. If all goes well, Firefox may roll out the feature to all users in the stable version.
When HTTPS-only mode is enabled, Firefox loads HTTPS sites and resources as before. When an HTTP site or resource is detected, the browser will attempt to upgrade it to HTTPS. If the upgrade is successful, the site or resource will be loaded successfully; conversely, if it cannot be upgraded, the site or resource will be blocked, which may cause the site to be inaccessible or partially loaded. When the upgrade fails, Firefox will also show the user a “Secure Connection Failed” error message.
For Firefox users running Firefox 76 Nightly, you can activate the new HTTPS-only mode in your browser in the following ways:
- Load about:config in the browser’s address bar.
- Confirm that you will be careful.
- Search for dom.security.https_only_mode using the search field at the top.
- Set the preference to TRUE to enable HTTPS-only connections in Firefox.
- Set the preference to FALSE to allow all connections (default).
Currently, although most sites already support HTTPS, some sites still use HTTP. According to Mozilla’s statistics, HTTPS accounts for only about 82% of all Firefox connections.