Qualys BrowserCheck is a free tool that scans your browser and its plugins to find potential vulnerabilities and security holes and help you fix them.
Browserscope is a community-driven project for profiling web browsers. The goals are to foster innovation by tracking browser functionality and to be a resource for web developers.
Panopticlick checks if your browser’s configuration is unique. The more unique your browser, the less easily it could be tracked. Web tracking is a privacy risk for users.