Hmm, some interesting developments:
It appears that URL re-writing is the issue, specifically the part that forces login via HTTPS. If I disable those rewrite rules, I can successfully login and see my wiki pages. I found a few differences between my rules and the ones on the dokuwiki website, but that didn't fix the problem. Then I discovered that with the rewrite rules disabled, if I manually changed the URL to use the HTTPS protocol, I get the exact same error message ("Firefox cannot contact localhost") as with the rewrite rules enabled. I'm fairly confident that it isn't a problem with my rewrite set-up, since my other rewrite rules work correctly (the ones that make the URL's look nicer). Anyone have any ideas?
My "Force Login via HTTPS" rewrite rules:
RewriteEngine on
RewriteBase /dokuwiki
##### Force login over HTTPS #####
# Switch to secure on login, profile and admin actions
RewriteCond %{HTTPS} !on
RewriteCond %{QUERY_STRING} do=(log|profile|admin)
RewriteRule ^(.*) https://%{HTTP_HOST}/$1 [R,QSA,L]
# Change back to non-secure on show action
RewriteCond %{HTTPS} on
RewriteCond %{QUERY_STRING} (do=show|^$)
RewriteCond %{REQUEST_METHOD} GET
RewriteRule ^(.*) http://%{HTTP_HOST}/$1 [R,QSA,L]
Cheers,
red