You could start by explaining how a privacy focused nonprofit is marginally worse than a multi-billion dollar advertising company with regards to privacy.
If a tobacco company makes a donation to a cancer research charity, do we now hate the charity?
That's a gross misrepresentation.
Mozilla was an investor in Cliqz, so it's not precisely a full-on third party. And the data was (at least, according to the article) well anonymized.
I can see why Moz would want to try and keep up with the user advantages of collecting this information -- catching malicious URLs, etc -- but even if it's just appearance-wise, they've lost a bit of trust here.
Frankly I think they should have two distributions of Firefox, one that's bells-and-whistles for the best user experience, and another that takes a more aggressive pro-privacy stance. This can be little more than the set of preinstalled extensions + default config.
Mozilla does not have a history remotely related to any sort of privacy violations, except in the eyes of those who think that literally anything to do with "telemetry" or "advertizing" is automatically evil.
Problem is, you can have non-privacy-invasive and non-malicious telemetry and advertizing.
Google and Microsoft are particularly nasty in this regard. But don't extrapolate their behaviour onto Mozilla.