From FCKeditor Docs

Browsers

CKFinder is compatible with the following browsers, with their default settings:

• Internet Explorer 5.5+
• Firefox 1.5+
• Safari 3+
• Opera 9.5+

Note for Opera: By default Opera is configured to not allow scripts to receive right click events. The context menu will not work because of this. To correct it, just enable this option in the Opera settings: Tools (Menu) > Preferences... > Advanced (Tab) > Content (Left List) > JavaScript Options... > Allow script to receive right clicks (must be checked).

Server

The following is the requirements in the server side for CKFinder for ASP.NET:

• A web site configured in Internet Information Server (IIS).
• The .Net Framework 2.0+ enabled in the web site.