If you add the handler from the KB you will be able to use all files with their original extensions as well as with sflb.ashx
extension that Sitefinity appends.
Let's say you have: Image.sflb.ashx.
If you try to call the image like Image.jpg you will get an error - not found.
after applying the KB: you can call Image.jpg as well as Image.sflb.ashx.
The solution just checks the mime type required item.
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