I wasn't involved in the study on this. I watched a presentation summarizing the study.
User research isn't my field, but my understanding is that the study asked a random sample of people if they noticed the feature, if they found it useful, how they used it, and so forth.
Did you also consider if this "benefit" will conflict with the Mozilla Manifesto or not? What were the arguments pro or against of it?
If you did perform this analysis, then was it performed before the user study or after? If you did not, then why?