"Why would the site author get to decide what the value should be?"

I didn't realize site's more liberal referrer policy could override, but the common use case for site specifying a restrictive referrer policy is an intranet where existence of a URL might leak info, including to competitors.

I'd like Mozilla to be more aggressively pro-privacy and free software than it is on all the things, but I don't think there's anything unusually nefarious going on here, just the normal level. I recall in the 1990s everyone knew the full URL was sent as referer, didn't give it a second thought or have privacy even cross our minds, and built applications expecting to utilize the referer. I'm pretty sure I did that several times. I was naive for sure. I guess that some applications still rely on that behavior and that turning it off abruptly would cause users to be frustrated and Firefox to lose market share. Same winning argument as for supporting encumbered media formats and DRM. Sigh.