Firefox suddenly blocking popups from allowed sites

[Patrick Wiseman]

My Firefox, as reported by "About: Firefox":

Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.0.1) Gecko/20060313 Debian/1.5.dfsg+1.5.0.1-4 Firefox/1.5.0.1

I have some pages which popup information boxes when the mouse is over certain words.  These have been working flawlessly, but suddenly Firefox is blocking the popups.  The sites _are_ in my list of allowed sites.  It is _not_ blocking onClick popups from the sites, only onMouseOver popups.  Any ideas?

Thanks
Patrick