I get your point, but this feature is being pushed to users prominently, and it turns out it doesn't do anything with the search results on both Youtube and Amazon, which are pretty much THE most likely sites you could think of, that anybody's going to be using. That seems like a pretty glaring omission to me.

There are lots of bug reports already opened about it not working as intended on various large sites, including Facebook, Google Images etc.

It's pretty obvious to me that such sites are going to keep changing their parameters because they're privacy predators. If Mozilla is not willing or able to keep the parameter definitions up to date then this feature can end up doing more harm than good.