But a request is still a request. It might not make sense to include referer data in the case you mentioned but that does not mean every cros request will fit that description.
There are no such cases, period. Also, with an exception of dumb content protection schemes (anti-hot-linking), Referrers are used exclusively for tracking purposes and carry zero positive benefits for the users. If Mozilla is in fact "passionate about putting its users first", these headers must go. It is as simple as this.
I run a small site, and we would occasionally get hotlinked by random people searching for images on Google, which would kill our bandwidth caps. If it weren't for referer filters, we'd have to hide any image for unregistered users.
That said, keep just first-party referers would be fine - we'd just block any image request without referer.
1) If you came from a social media site, maybe I'd highlight that particular social sharing option in a share bar, or hide others.
2) In an e-commerce store, maybe Google sent you to some page on my site that isn't really the best for your search term (product discontinued, other better matching product), I can give you a link to that other page. Google isn't necessarily magical in its ability to pick the best page on a site for a specific term. Maybe if you come from a competitor I can highlight some content that compares my product to the competitor's.
3) I've never derived a ton of benefit from it, but some sites will highlight your search term for you on a page. It could possibly also automatically scroll you to a relevant section if it's a long page and what you searched for is an exact match for some subsection.
In general it can be a valuable data point sites can use to improve the end-user experience. That being said, I can't think of anything where the value really outweighs the potential for abuse, but I think saying that it has no value to the user is short-sighted.
Referrers are used exclusively for tracking purposes
and carry zero positive benefits for the users.
You may disagree that is a better experience for you, but you may not make blanket statements that "there are no such cases, period".