> Do you now see what I mean? It is not that your financial institutions would zero-day you, it is that you'd use the secure-but-slow browser (or browser mode) to access those sites. Secure, because you're dealing with financial data. Slow because that is what the parent poster stated as the price he'd be willing to pay for a secure browser.
I understood what you meant the first time. Again, the risk you're mitigating is one that simply doesn't exist. A slow but hardened engine protects against attacks that simply don't happen for the sites you're talking about.
The threat here is abuse of the JS engine. If you're on my bank website origin running slow JavaScript you can already steal all of my money. Hardening the JS engine for that site is pointless because any bad JS running on the page already has the literal most valuable thing I have: access to all of my money. Having a provably not-zero-day-able browser does nothing to mitigate an attack if there's bad code running on the page.
I understood what you meant the first time. Again, the risk you're mitigating is one that simply doesn't exist. A slow but hardened engine protects against attacks that simply don't happen for the sites you're talking about.
The threat here is abuse of the JS engine. If you're on my bank website origin running slow JavaScript you can already steal all of my money. Hardening the JS engine for that site is pointless because any bad JS running on the page already has the literal most valuable thing I have: access to all of my money. Having a provably not-zero-day-able browser does nothing to mitigate an attack if there's bad code running on the page.