So how do you want take web forward without testing new things based on real life data? Did you even read what they want to do and how they are going to do it?
Seriously they have to? Isn't this obvious enough? When downloading TEST RELEASE you willingly accept that it will collect anonymous data and send it to them. If you do not want to test something, because you're opposed to it, do not do it.
A lot of companies do that and I do not see anyone complaining about it for example Apple and macOS betas.
I just received this email from my bank. Something like this would be nice:
"Below is a link to the 2018 Annual Privacy Notice. This Notice provides details on the types of information we collect, why we collect it, and with whom we may share it. Collecting and permissible sharing of your information allows us to offer you a comprehensive range of services to help you meet your financial goals. "
Yes, for stable version if they want to track something more. But we are talking about test version. You accept this when downloading "Firefox Nightly automatically sends feedback to Mozilla.": https://www.mozilla.org/en-US/privacy/firefox/#telemetry
How you want to improve something without data? Based on intuitions?