Serving RT with Nginx: Firefox refuses to log in

Hello list,
I have 4.2.8 (the latest version available as a package for Jessie) running
through Nginx. I can get to the main page through, which is
good, but I can’t log in with the default information. When I do, Firefox
gives me an error:

The page isn’t redirecting properly
Firefox has detected that the server is redirecting the request for this
address in a way that will never complete.

I’m following the Nginx setup instructions here:

It’s a bit confusing as my paths are different
(/usr/share/request-tracker4) but things seem to be working. I just don’t
know why this problem is popping up. It could be an Nginx thing, but
configuring RT is the first time I’ve ever seen it, so I thought I’d ask
here first. Thanks.

Alex Hall
Automatic Distributors, IT department