Thanks to Eric, who today made me aware of a problem when using Wizz RSS and Tab Mix Plus – http://wizzrss.blat.co.za/2010/09/08/wizz-rss-40-beta-maxversion-bumped-to-40b5/#comments.
If you are one of those who use Tab Mix Plus and Wizz RSS, don’t worry, you haven’t gone crazy 
There is some pretty serious weirdness when both add-ons are enabled.
Eric reported the problem in the Tab Mix Plus support forum, and onemen (one of the Tab Mix Plus developers I assume) has undertaken to sort out the problem on the Tab Mix Plus side. Thanks onemen!