An important feature of Firefox that isn't nearly as well known as it should be is first party isolation.

It can be a bit annoying due to eg Recaptcha, but it works fine 99% of the time. Some sites will break, but these are far and few between. I just use another browser for those.

It was upstreamed from TOR and will scope all data (cookies, caches, etc) per domain. It's not a panacea, but definitely a good step.

(about:config , privacy.firstparty.isolate)

I feel like something like this should be the (standardized) behaviour of browsers. Sharing any kind of observable state between domains should require an explicit opt-in with a prompt.

Like: "Privacy Warning: techcrunch.com wants to share your data with facebook.com. Do you want to allow this?"

(such fine grained permissions are a complicated topic of course, but that's a longer discussion...)