Firefox's Optimized Zip Format
> At the time optimized jar change broke antivirus scanners, which further sped up Firefox startup :)<p>I'm pretty sure that counts as cheating.<p>AV overhead is a real issue though.  I was recently copying a directory full of small files from one fast SSD to another (larger) one.  I started the transfer and Windows estimated about 8 hours to finish the transfer, and the overall progress seemed to be roughly on track.  On a whim I tried temporarily turning off Microsoft's built-in antivirus scanning.  Total transfer time dropped to about 40 minutes.