support for websockets compression using permessage-deflate
Chrome and Firefox support the standards based websockets compression extension permessage-deflate during protocol upgrade negotiation (see https://tools.ietf.org/html/draft-ietf-hybi-permessage-compression-17).
Applications that use websockets with a reasonable payload across a LAN (eg. most JSON payloads) and especially across the internet are noticeable slower in Edge.
As more modern web apps (SPAs especially) implement websockets, Edge is at a disadvantage compared to competitive Windows browsers.
Please consider for a future update of Edge.