Your changeset is not directly a patch for GIFReadWriter>>readBitData, it looks like you uploaded
your (subclass) debug code with a class WizAnimGIfProbe including log stream stuff, ...
However by patching the original method with the essential fix:

initCodeSize := self next.
bitMask := (1 bitShift: initCodeSize) - 1.

Squeak correctly displays http://www.mathconsult.ch/showroom/unipoly/anim24.gif
but not http://www.webdeveloper.com/animations/bnifiles/disco_anim_bf16.gif 

BTW: since Squeak is able to display images when they are dragged from a browser onto
the morphic world it would be nice to keep animated gifs animated after dragging.

Bye
Torsten
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