Disable HTTPS-only mode in Unsafe Browser

The Unsafe Browser is configured to use the HTTPS-only mode of Firefox:

Captive portal are not supposed to capture HTTPS:

HTTPS web sites are now more or less a standard and to maintain security and user confidence it is essential that captive portals DO NOT attempt to capture port 443. »

https://nodogsplashdocs.readthedocs.io/en/stable/faq.html#is-https-capture-supported

So, when using a captive portal, people end up on "Secure Connection Not Available" instead of being displayed the HTTP version.

We should disable HTTPS-only in the Unsafe Browser.