This add-on displays web vulnerability information from PunkSPIDER about the site you’re currently visiting. PunkSPIDER is an open source project that scans the entire Internet for web vulnerabilities and provides the results free and open to the public.
Here is a little more about the add-on and PunkSPIDER project:
PunkSPIDER is an open source project that is performing a vulnerability analysis of websites across the entire Internet. It checks for 7 types of basic vulnerabilities that, if present, could make a website particularly dangerous to the security and privacy of users. The results are published in a searchable repository where users and website owners can check if specific websites they use / own are vulnerable to these common attacks. A vulnerable website can lead to your personal information being stolen, which can lead to identity theft and credit theft. Moreover, vulnerable sites can be used to spread malware and all kinds of nasty stuff to your computer.
Want to check out more about this add-on? You can find PunkSPIDER at the Firefox Add-ons website.