New compression from Google - better than gzip. Supported in Chrome and FF. See site https://www.netwarc.nl/ for an example. Fiddler is unable to decompress the response content.
Also see http://www.omgchrome.com/brotli-http-compression-coming-to-chrome/ and https://textslashplain.com/2015/09/10/brotli/
Including Brotli by default is on our list already,
Fiddler works fine with Brotli, just install https://textslashplain.com/2016/01/27/automatically-evaluating-compressibility/ or drop brotli.exe in the \Tools\ folder.