If the site isn't redirecting the page, I wonder whether an add-on is doing it for some reason. A standard diagnostic to bypass interference by extensions (and some custom settings) is to try Firefox's Safe Mode.

First, I recommend backing up your Firefox settings in case something goes wrong. See Back up and restore information in Firefox profiles. (You can copy your entire Firefox profile folder somewhere outside of the Mozilla folder.)

Next, restart Firefox in Firefox's Safe Mode (Diagnose Firefox issues using Troubleshoot Mode) using

Help > Restart with Add-ons Disabled

In the dialog, click "Start in Safe Mode."

If the site works correctly, this points to one of her extensions or custom settings as the problem.

To also disable plugins, she can try here:

orange Firefox button or classic Tools menu > Add-ons > Plugins category

Any change?

You may have visited that website in the past via the ftp: protocol and in such a case Firefox might prefer some protcols if auto-fill is enabled.

Try to set the Boolean pref browser.urlbar.autoFill to false on the about:config page.

See "Prevent Firefox from automatically completing URLs":

• https://support.mozilla.org/kb/search-your-bookmarks-history-and-tabs-awesome-bar