I\'m playing with the idea of making a completely JavaScript-based zip/unzip utility that anyone can access from a browser. They can just drag their zip directly into the br
Your problem essentially boils down to "not all browsers will support this".
You could try a workaround and serve the unzipped files from a Flash object, but then you'd lose the JS-only purity (anyway, I'm not sure whether you currently can "drag files into browser" without some sort of Flash workaround - is that a HTML5 feature maybe?)