Backed out for causing for causing dt failures on browser_net_copy_as_powershell.js

• Backout link
• Push with failures
• Failure Log

Trivial fix; just needs ", zstd" added to some canned response headers it compares to

https://hg.mozilla.org/mozilla-central/rev/68f119112940
https://hg.mozilla.org/mozilla-central/rev/99e71b905661
https://hg.mozilla.org/mozilla-central/rev/ac55c45e0d0f

This needs to be documented at https://github.com/mdn/browser-compat-data/blob/ae0b3849fc709af63e04e78cdd24dc2eda22efad/http/headers/Content-Encoding.json#L100.

Sebastian

:jesup could you consider nominating this for a release note? (Process info)

FF126 MDN docs for this can be tracked in https://github.com/mdn/content/issues/33086.

As far as I can tell this is just a BCD entry in Content-Encoding (done) and a release note.

Is only Content-Encoding affected? I mean is zstd used for anything else? What about Accept-Encoding (my assumption is that this is set by the browser, and you normally wouldn't get back zstd if you had not set this?)

Note, have marked as dev-doc-complete on assumption there is nothing else to say.

Release Note Request (optional, but appreciated)
[Why is this notable]: Significant change in what types of compression we support, impacts websites
[Affects Firefox for Android]: yes
[Suggested wording]: Firefox 126 supports Content-encoding: zstd (zstandard compression). This is an alternative to broti and gzip compression for web content, and can provide higher compression levels for the same CPU used, or conversely lower server CPU use to get the same compression. This is heavily used on sites such as Facebook. It shipped in Chrome 123 recently.
[Links (documentation, blog post, etc)]: RFC 8878, http://facebook.github.io/zstd/

Renamed so it's clear that the actual support landed in this bug.