Since Firefox 83, users of Mozilla's Web browser have the ability to enable an "HTTPS-only" mode. When this feature is enabled, Firefox will attempt to automatically load the secure version of the site you wish to view when it exists.
Open a Firefox window and click on the main menu shown by three superimposed lines. Then go to the Options menu to access the browser settings.
In the Firefox settings window that appears, go to the Privacy and Security section in the left column.
Then scroll down to the bottom of the window to see all the options displayed. You'll find the options related to HTTPS Mode only.
If you happen to come across an unsecured site that does not support HTTPS, Firefox will not load the page on your machine and will display a warning window.
You may, if you wish, and with the risks that this may involve, choose to Continue to HTTP site, which will temporarily disable the HTTPS-only mode you have enabled.
You will also be able to click on the lock icon in the Firefox address bar to directly manage the activation of this function in the browser.