I just tried the free option (bitwarden) and then migrated to Proton to use all of their apps. TOTP support is also an added bonus for the Proton Pass since Authy has fucked off a cliff.
It’s a rootkit. When it runs it basically has complete access to your system. You’re at the mercy of the guys at Riot and pray that no one breaches their system.
Not necessarily announce their existence. There’s some way for websites to communicate with extension like explained here. IMO, a sufficiently motivated actor can use this to add additional data point for fingerprinting.
Although most of the methods are only applicable if you’re using Chrome or Chromium based browsers and Firefox has disabled the methods commonly used to extract information from the browser.
I go the other way. My youtube account is used across my family. My recommendation is a fucking mess.