When using iNotes 8.5.2 Fix Pack 2 (or earlier releases) in Firefox 4, users see the following error messages either at login (if using Full mode) or when composing a new message (if using Lite mode)

Full mode

"uncaught exception: [Exception... "Component returned failure code: 0x80040111 (NS_ERROR_NOT_AVAILABLE) [nsIDOMHTMLDocument.createElementNS]" nsresult: "0x80040111 (NS_ERROR_NOT_AVAILABLE)""

Lite mode

"FKS is null"

These errors are related to the removal of remote XUL support from Firefox 4. According to Mozilla Bug Report #546857, remote XUL originating from Web pages is no longer supported. This change impacts Lotus iNotes 8.5.2.2 and earlier releases because iNotes uses remote XUL in several places to create an improved Firefox visual experience and to enhance feature capability.

This issue is addressed by Interim Fix 401.8HF6 for iNotes 8.5.2 Fix Pack 2, which introduces support for Firefox 4. This interim fix is available for download from Fix Central. See the following technote for more details:

Technote #1474006 -- Firefox 4 support availability for Lotus iNotes

Workaround
An unsupported workaround for this problem is identified within Mozilla Bug Report #546857.  Using the Remote XUL Manager add-on allows Web pages to continue using remote XUL. NOTE: Use of this add-on should be considered carefully since it modifies the intent behind Mozilla's removal of the remote XUL support.