Rich Text Editor Hangs and prevents editing - Firefox 12.0 Windows XP Prof 2002 SP3

Whenever I try to use the quick reply feature, the editor allows me to type but prevents any modifications.
I also observe this while trying to create new threads. I am able to enter the title but the editor doesn't allow me to post/edit the body.

I selected basic editor under general settings and it seems to be working fine. But any help to resolve the issue with the Rich text editor (WYSIWYG) is much appreciated :)

Environment : Firefox 12.0 running on Windows XP Prof 2002 SP3
Anti virus : Symantec End point protection

I am unable to type anything into the Quick Reply Text editor and Advanced Editor. They seem like it is disabled. This problem happens only in Firefox 16.
Attachment 1725
Attachment 1726

The Quick reply editor should be fine now after the y'day upgrade.

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