I've written a nice little application that goes through a Firefox cache folder and tags each file with an appropriate extension. It does a wonderful job so far, pulling out many kinds of images and text types. I can manually identify some Office docs, too, but those are harder to do automatically because there aren't 'magic bytes' at the top, and all I'm parsing is the first line.

Anyway, I've come upon a few binary files that I can't seem to identify or open. They all start with the bytes 1F 8B 08 00. The first 2 bytes seem to indicate a GZip file type, but that would be a bit surprising first off all. And second, it won't open them anyway (no archive program will). And IrfranView does a good job of recognizing misnamed extensions, and it doesn't know this one either.

Anyone with enough experience or understand what I'm talking about to offer a suggestion?