Enable Brotli Accept-Encoding/Content-Encoding
Ported bugs: 366559, 1211916, 1211580
Tested and it works like a charm!
Test page: https://www.iisbrotli.com/support
- Default Gecko Compatibility which is Gecko slice added to Native (for web compat)
- other modes pure native (no gecko slice) and Firefox compatibility (Gecko+Firefox+rv: changed to Firefox compat version)
This removes `general.useragent.compatMode.firefox` and `.gecko` in favor of an int pref.
See also: MoonchildProductions/Pale-Moon#466