Depending on what tactics you use, your passwords might be great or they might be awful. One thing is certain, though: if you reuse the same password across multiple websites, that is definitely a bad idea. Mozilla are keen to show you just how bad.
If you use the same password across multiple websites, and one of those sites has its security breached, you may find yourself with a problem. Mozilla's new Firefox add-on is designed to show you how bad the problem could get. Mozilla explains:
With this add-on, you can visualize your passwords and the sites you use them on. By looking at this visualization, you can get a quick idea of which passwords you've been using the most, and the kinds of sites you're using them on. As you continue to change your passwords and update your password manager, the picture will improve!
But Mozilla, I spotted a problem! You're using passwords saved on the computer to generate these visualizations. As soon as you save your passwords, it's game over. If someone steals your laptop, bad luck: those passwords can be recovered even if the thief can't log-in to your user account. So, uh, neat work Mozilla, but readers, I do hope you can't take advantage of it. [Mozilla]