In double checking, at least it appears that they don't do this for some of their mailing lists; the mozillians.org stuff appears to have unmolested links.
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.
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.