They could probably raise more if Google went away
I'm interested in how you think Mozilla would raise more than half a billion dollars if they didn't take any money from Alphabet/Google. Genuinely. In what ways could Mozilla raise money that they're not doing right now?
Maintaining a browser that doesn't rely on someone else's upstream code is quite an ordeal. Of the four main browsers (Chrome, Edge, Safari, Firefox), 3 are built by large for-profit enterprises and the other relies on money from a large for-profit enterprise. Browsers are very complex pieces of technology and can't be maintained by 3 guys on GitHub in their spare time.