[Osmium]

Yep. Doing this on OS X and launching it via Alfred. I'd rather not share the script solely because I don't want to be responsible for some bug or bad idea that could cause you or anybody else problems.

However, I can share some inspiration to get started:

SuperGenPass (the original place I saw the idea): http://supergenpass.com

A fork of SuperGenPass using bcrypt/base85: https://github.com/cmcnulty/SuperGenPass

I wouldn't use either of the above because they're JavaScript-based, but someone has implemented it in Python: https://github.com/gfxmonk/supergenpass

I took that script as inspiration, modified it to use bcrypt, and then used the Python "keyring" module for access to the OS X keychain, and calling "osascript" to use an AppleScript one-liner to get Safari's front-most URL as an input.

It does potentially have the side-benefit of protecting against phishing attacks too, since if the domain is different, the password is different, so you can't be fooled into giving your password to the wrong website.