I configured Mediawiki 1.5.7 to use the REMOTE USER authentication method described here:

http://meta.wikimedia.org/wiki/Auto_Login_via_REMOTE_USER

If a user logs on under Windows with Internet Explorer and attempts to delete or update a file, it works without problems. This Windows/IE user is logged onto the corporate domain controller, so he is not prompted for username/password upon entering the Wikimedia site.

However, if a user logs on using Mozilla Firefox, the same action reports the following error message:

"Internal error There seems to be a problem with your login session; this action has been canceled as a precaution against session hijacking. Please hit "back" and reload the page you came from, then try again."

Going back and refreshing still has the same problem. I've also noticed that IE users who did not initially log on to the Windows domain (so they're prompted for username/password upon entering the Wikimedia site) experience the same problem.

I enabled debug logging, and this is what it reports after pressing "Confirm" to deletion:

Start request POST /mediawiki/index.php? title=Image:blah.gif&action=delete Host: blah-machine User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.12) Gecko/20060130 Red Hat/1.0.7-1.4.3 Firefox/1.0.7 Accept: text/xml,application/xml,application/xhtml +xml,text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5 Accept-Language: en-us,en;q=0.5 Accept-Encoding: gzip,deflate Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7 Keep-Alive: 300 Connection: keep-alive Referer: https://blah-machine/mediawiki/index.php? title=Image:Snl_tbird_logo_trans.gif&action=delete Cookie: tz_offset=-28800; mediawiki_dbUserName=BlahUser Authorization: Basic Content-Type: application/x-www-form-urlencoded Content-Length: 73

Main cache: fakememcachedclient Message cache: mediawikibagostuff Parser cache: mediawikibagostuff Using reader #0: localhost...

Block::load: '192.168.3.2', '34', 1 ** no caching ** WARNING: Abrupt exit in /data/www/html/mediawiki-1.5.7/includes/GlobalFunctions.php at line 437 WARNING: Abrupt exit in /data/www/html/mediawiki-1.5.7/includes/OutputPage.php at line 726 WARNING: Abrupt exit in /data/www/html/mediawiki-1.5.7/includes/ImagePage.php at line 402 WARNING: Abrupt exit in /data/www/html/mediawiki-1.5.7/index.php at line 179

Does anyone have any suggestions? Thanks.