Do you reuse passwords across multiple websites? The habit is alarmingly common, despite being a well-known security risk. You know how the warning goes: If you use the same password across a number of different websites and one of those accounts is compromised, some evildoer could infiltrate the other sites, potentially exposing a wide range of personal data and even putting one's finances or identity at risk.

Mozilla knows all too well the online privacy and security issues that its users face. Its Firefox browser is the gateway to the Web for millions of people, and it doesn't take that responsibility lightly. Mozilla Labs recently launched what it calls the Watchdog initiative to help users understand and manage passwords and privacy-related matters.

The latest Watchdog project to see the light of day is a Firefox add-on called the Password Reuse Visualizer. Once installed, it allows users to see a data visualization of their stored passwords and how they're being used across sites.

The visualization also shows relationships between similar passwords, even if they're not the same.

"Some users like to make many slight variations on the same password," wrote Watchdog developer Paul Sawaya. That's fine, but still an example of password reuse. When the visualization detects two similar passwords, it connects them with a square orange node."

The idea is to help users understand how widespread their password reuse is so that they can put the effort into make things right.

Unfortunately, those with the worst password security habits of all are probably unlikely to download a Firefox add-on like this and use it. Still, anything Mozilla can do to generate awareness about Web security issues is a worthwhile effort.