I know this is old, but a lot of people still don’t know about it.
It can test for up to date Mozilla, Opera and Internet Explorer flaws, exploits and vulnerabilities.
Browser vulnerabilities are a serious issue now.
You can see which vulnerabilities they test for here and the statistics of the tests results here.
Total tests finished: 739828
Tests that found high risk vulnerabilities: 219614
Tests that found only medium or low risk vulnerabilities: 82803
Tests that found only low risk vulnerabilities: 9493
Tests that found no vulnerabilities: 427918
The FAQ is here.