The Price of Free Google Report.
Proton analyzed over 54,000 demographic profiles using 2025 ad auction data to estimate what advertisers pay to reach different types of Americans. The range is much wider than you might expect.
The average American generates about $1,605 a year in advertising value. A 35- to 44-year-old man in Bozeman, MT, without children, using a desktop and making high-value corporate searches, generates an estimated $17,929.30. An 18- to 24-year-old father in Fort Smith, AR, using an Android phone and making low-value searches, generates $31.05.
That’s a 577x difference between two people using the same free service.
Why would it be trivial for them to get access to your browser?
Because any webpage you load has total control of the content it serves, including the plaintext of your emails along with the keys you use to decrypt them.
e2e encryption in browser is effectively not e2e in any meaningful sense, this goes for any thing, but Proton are the worst for trying to convince you that they can't do this.
Software that is targeting people who might need encryption should be honest about it's own limitations.
I'm still not clear how they would access it.