This thread (http://www.dynamicdrive.com/forums/showthread.php?t=4861) points out a bug (and its solution) in Blending Image Slideshow Script (http://dynamicdrive.com/dynamicindex14/image4.htm) in Opera for which the script is rated. Since Opera sees 'document.all' as true, it tries to apply the IE only filters to the images, causing an error that stops the script in the Opera browser.
Thanks Jscheuer. I'll look at updating the script soon for this fix.
The better fix would be to drop the browser detection (by object inference) altogether and use feature detection: if there is a filters property, manipulate it.
Opera isn't the only browser to implement the all collection which is why object inference, just like user agent string parsing, is flawed and should be avoided.