Firefox's HTTPS-only warning page isn't suitable for Tor Browser

Currently, if you try and visit a HTTP website, like http.badssl.com, you get a warning page. But the text of the warning page comes from Firefox, and is not really suited for Tor Browser.

Currently it says

HTTPS-Only Mode Alert

Secure Site Not Available

You’ve enabled HTTPS-Only Mode for enhanced security, and a HTTPS version of http.badssl.com is not available.

The first part should probably be more like

HTTPS-Only Mode is enabled in Tor Browser for enhanced security

since it is not a user choice to turn this on. Plus, the second part should probably be

a HTTPS version of http.badssl.com was not found.

since the HTTPS version could be available on another circuit (or it may have been triggered by a timeout as in #41068).

In addition, the "Learn More…" link takes the user to https://support.mozilla.org/en-US/kb/https-only-prefs which includes a good explanation of HTTP vs HTTPS, but it has no Tor Browser or network context and gives instructions on how to turn on or off https-only mode.

Finally, we should probably let the user know that sometimes reloading the page with a new circuit can establish a HTTPS connection (e.g. if your current exit node is bad), and perhaps give them a button to do so.