This extension generates a password from a website domain & a personal password.
Like most folks on the internet these days, I have more logins than I can possibly remember. Usually, that means people are going to use the same password for a bunch of different sites. The problem, of course, is that if one site's database of passwords is compromised, you're vulnerable. You can use a password management tool, but then you have to either keep it with you on a flash drive or trust one site with all of your passwords (and lose access when you don't have an internet connection).
You can use the web version anywhere (including your smartphone or tablet), and download the extension (which pulls the url from your current tab) for your personal computers.