I think of this as no more invasive than pre-caching stuff in a page when you see links that are likely to be clicked, or any other browser optimization.
I may be pounding my fist later if the results don't look great, but ultimately, I think Mozilla's heart is in the right place.
I can think of tons of ways to work around this if I thought it was a real issue, I don't. People who want to block analytics, trackers, ad networks, etc... know how, and this doesn't feel like it is targeted at those people, or even squarely at the tracking pixels.
HN-pre-emptive-defend-myself: My company doesn't share or sell data with third parties (it's in our TOS – and could obviously change in some Orwellian future, but we'd have to update the TOS), it's the customer's data, they can use it in the same way they'd use any other data they collect. We don't do cross-domain tracking, or aggregate behavioral information across customers, and the way we've built it, it makes it pretty hard to tie any two visitors together across sites if you were to hypothetically acquire our dataset. We're also working on building tools to comply with GDPR and wipe out data per-request. Anyways, I think a lot of very bad actors have made the space have a bad reputation and I don't blame anyone for blocking everything, or even for hating my company, or generally all analytics.