You don’t need $500M per year, by far, to continue developing a web browser. Mozilla is conducting all sorts of operations that have little to do with that core task.
Wikimedia is often criticized for asking for donations, while having millions in the bank, but this is exactly why. Mozilla should have taken all the money they could from Google and others, focused on Firefox and MDN (and perhaps Thunderbird) and just continuously saved and invested whatever was left. If/when donation dry up, Wikimedia will hopefully have saved up enough to fund Wikipedia for decades. Once Mozillas income is gone, there's no backup.
Mozilla spend all the money they could each fiscal year (I don't actually know, I didn't check their budgets), trying to build products that would fund the project into the future. It's just that none of those projects made much sense, nor where they ever going to bring the the amount of money required, which really seems obvious from the outside. I can see the VPN maybe bringing in a bit of money, but no where near enough.
> Wikimedia is often criticized for asking for donations, while having millions in the bank, but this is exactly why.
You are omitting the part where Wikimedia spends large parts of that donation money on things barely related to Wikipedia. Not to mention inflated salaries throughout the organization.
Once this stops, there’s no way for us to keep funding operations at the level they’re at.