I think that's dependent on what is stored. Sure the link enables them to capture a whole lot of data, but if an agreed standard of 'tracking data' was all that was stored. I think that would be an improvement.
EDIT: Similar to how we capture credit cards. Often the provider could capture and store everything, and publish it online if it liked. But generally (due to law, and standards) they are either passed off to a payment provider or stored with a certain level of security.
I don't think it is necessary in this case for Mozilla to even be in possession of transiently-non-aggregate data, though. If they want to analyze click-through rates or whatever, they can have URLs that are constant across users and not lose any data. For credit cards, the payment processor must have the unique card information, so collection is warranted in that case, even if they are never stored.
That is: since I have no insight into what happens to the data once it reaches their servers (outsourced to an external analytics platform), I object to them collecting it unnecessarily in the first place. Storage does not come into play, since while I trust Mozilla I don't trust the third-party, no matter how much Mozilla claims to have vetted them.
EDIT: Similar to how we capture credit cards. Often the provider could capture and store everything, and publish it online if it liked. But generally (due to law, and standards) they are either passed off to a payment provider or stored with a certain level of security.