Release Note Request (optional, but appreciated)

[Why is this notable]: This is a new web platform feature and developers would be interested in the support of this feature.

[Suggested wording]:
Added support for the No-Vary-Search HTTP response header for the HTTP disk cache. Servers can now declare which URL query parameters are irrelevant to the response, allowing Firefox to reuse cached resources across parameter variations and improving cache hit rates.

[Links (documentation, blog post, etc)]:

https://httpwg.org/http-extensions/draft-ietf-httpbis-no-vary-search.html

[Tracking Requested - why for this release]: enable no-vary-search for release users.

We need to flip the pref.

Does it have a webcompat impact? It was recently activated in nightly and it doesn't seem that there are metrics set up to study the use of this header as Bug 2038028 is not fixed.

I would say the webcompat risk is minimal here as failure to support or improper handling this will only lead to more network requests.
I also have a patch for Bug 2038028 (which can easily uplift).
However, I am okay in differing this to 154 if you insist as we don't have a hard target for 153.

If we don't have a strong reason to backport to older branches, I don't think we should uplift it, it would also need to land first on main.

https://hg.mozilla.org/mozilla-central/rev/50b5c7edffea

Added to the Fx154 nightly release notes, please allow 30 minutes for the site to update. This will carry over to the final Fx154 release notes.