Personally, I use it as much for other secrets as for browser passwords. Social security numbers, software licenses (not so much anymore), password reset questions, passwords I can't paste (for work), etc.
I don't use a plugin. Never tried it, simply never mattered enough (and I generally store frequently-used browser passwords in the browser's keychain as well).
Genuinely curious: why would you pay for 1Password but then use your browser's password manager? Now you have to keep track of updating passwords in two places? Or remembering which sites are stored in which password manager? That's breaking my brain.