In my prior post I ran into a problem with FCKeditor on Apache having to do with serving JavaScript files as the proper MIME type. I ran into a similar problem with XML files when trying to load multiple instances of FCK textareas:
Error: this.DOMDocument has no properties
Source File: http://www.mysite.com/FCKeditor/editor/js/fckeditorcode_gecko.js
Line: 43
This is easily fixed in the same way, by telling Apache how to properly serve XML files. Put this in your httpd.conf or an .htaccess file:
AddType text/xml .xml

For some reason, FCKeditor would not load in Firefox 2.0 even though it loaded in IE just fine. Turns out Apache was serving up the javascript files as the wrong FileType, so Firefox would choke on some jibberish characters:
Error: illegal character
Source File: http://www.myserver.com/FCKeditor/editor/js/fckeditorcode_gecko.js
Line: 1, Column: 1
Source Code: /*
The fix is easy enough, simply add an .htaccess file to your dir containing the following:
AddType application/x-javascript .js
Now FCKeditor should work fine in Firefox.