Edited to add: I wrote a followup post to address comments here and elsewhere that advertising is working as intended. This paper has been reported incorrectly in several places as being about cookie blocking. Tracking protection blocks all traffic, not just cookies.
My paper with Georgios Kontaxis got best paper award at the Web 2.0 Security and Privacy workshop today! Georgios re-ran the performance evaluations on top news sites and the decrease in page load time with tracking protection enabled is even higher (44%!) than in our Air Mozilla talk last August, due to prevalence of embedded third party content on news sites. You can read the paper here.
This paper is the last artifact of my work at Mozilla, since I left employment there at the beginning of April. I believe that Mozilla can make progress in privacy, but leadership needs to recognize that current advertising practices that enable "free" content are in direct conflict with security, privacy, stability, and performance concerns -- and that Firefox is first and foremost a user-agent, not an industry-agent.
Advertising does not make content free. It merely externalizes the costs in a way that incentivizes malicious or incompetent players to build things like Superfish, infect 1 in 20 machines with ad injection malware, and create sites that require unsafe plugins and take twice as many resources to load, quite expensive in terms of bandwidth, power, and stability.
It will take a major force to disrupt this ecosystem and motivate alternative revenue models. I hope that Mozilla can be that force.