HTTP Compression was introduced to all the GMS interfaces in build 3075 and higher.
HTTP Compression means that the Web Server, (in this case the GMS WWW service) will compress data, and send a compressed page to the browser, which the browser will decompress and display. This reduces the amount of data to be transferred, and so will speed up the interface. The speed increase will be most noticable over slow connections.
You do not need to configure HTTP Compression, if your browser supports it it will be used automatically.