Try to set $wgScript to $wgScriptPath/wiki.php (or $wgScriptPath/wiki) or whatever you renamed that file to.
David J. Biesack wrote:
I have MediaWiki 1.4.0 on Red Hat 9, with PHP 4.3.10, mysql Ver 12.22 Distrib 4.0.23 and Apache 2. MediaWiki is functioning fine on my intranet, but we have performance problems with Firefox users. Page requests in Firefox are taking very long, whereas they are much faster with IE 6.