This is such a un-nuanced take.
In this case Firefox's route-to-market is the product. It's a distribution channel where some people who receive the free version will upgrade.
Free tiers for products where some will pay to upgrade seems like a reasonable compromise, but it does depend on how the deal is structured.
If Mullvad pays Firefox for the free users then Firefox's incentives are aligned with its users.
If Mullvad pays per conversion then it's a different story.