same javascript file, but different file size depends on a server?

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http://serverfault.com – I have a weird problem. I have two exact website on two servers - dev and qa. The dev one shows that my javascript size is 100kb, but the qa says 400kb. When I save the script on my local, it is 400kb. I looked at the header of the javascript on the dev and it looks like..it's sending "Content-Encoding gzip". What is this and how do I enable this on the qa to make my script smaller? (HowTos)