Brotli
From Just Solve the File Format Problem
Brotli is a compressed data format developed by Google. It is designed for a high compression ratio, and fast decompression. When used as a web content compression encoding, it uses
br in the Accept-Encoding header so that a browser can signal support; this support is present in newer versions of Firefox and Chrome as of early 2016.
While the addition of this format to Firefox/Mozilla was still under discussion, there was a bit of a mini-flap over earlier proposals to use "bro" as the encoding identifier (and file extension for Brotli-compressed files), as this was deemed by some to be misogynistic. After some debate over bro vs. brotli vs. br, the shorter of these was ultimately adopted.
Brotli files (and network traffic) do not have any magic bytes: the first bytes will have right-most bits from this table, which could be anything.
