Reading this, it would be interesting if we had some standard Privacy Tests for browsers. Much like perf & security, you take stock browsers and run them over a set of pages not known in advance, in a modified environment. Look at what happens on the network, disk activity, etc.

Publish the results on a regular basis. See how well all browsers do without turning knobs at protecting users from tracking, privacy leaks, fingerprinting, ad exposure, and the like. The pages could exercise common vectors, but vendors couldn't optimize for them.