That's a cool extension, but I can't see it gain massive popularity. There is a class of problems with it that wfor a site ould be solved if you make it a bookmarklet (with a companion site): does it support your browser, what if you need to log in from a computer that doesn't have this browser extension?

The real problem is that if you are security-conscious enough to understand how this works and why you need it, you are not using the same password over and over again. E.g. I have a "weak" password that I use on HN and many other sites, but my mail and sites that involve (even remotely) money get an individual password each.