Example: my main general browsing profile has flash, PDFs and all plugins disabled, absolutely all handlers switched off, all hardware access off, WebGL switched off, no account logins and uBlock Origin set to aggressively block most third-party requests.
My second most used context is for personal sites I login for - with access to third-party cookies (for those sites) and running most third-party requests with standard uBlock rules.
I have yet other contexts (Chrome profiles) where Flash is enabled if I need that, then a separate browser for Java etc.
I'd like to see these security levels built into browsers where the contexts are built around permissions and site trust rather than access to the user store (which is also important)
I don't think it's realistic for most users to do this right now with profiles, as it requires a lot of discipline - it needs to be in the UI.
Browsers have become as sophisticated as operating systems and we're accessing more and more of our personal data using them, yet the model of 'every site has access to everything' be it a site you trust, like Gmail, or a random URL you're clicking on - has somehow survived.
It's the equivalent of the old days where everyone would run their local systems with an admin account for everything. I really think browsers need a rethink along these lines where websites are treated like apps and you can apply a trust group to each.