From MozillaZine Knowledge Base
HTTP is the application-layer protocol that most web pages are transferred with. As part of the connection between client and server in HTTP 1.1, the client lists in what way it can/prefers to accept information (content negotiation). This preference controls which encoding types the application will report it supports.
Possible values and their effects
A comma-seperated list of encoding types with optional "q" (quality) values. A quality value says that the application prefers one type over another, but supports both. Quality values can be from 0 (not supported) to 1 (preferred format). If a quality value is omitted, it defaults to 1. Anything not listed is assumed to be not supported. Example:
First checked in
Present since at least 2001-05-11. Exact checkin date unknown.
Has an effect in