This morning I was trawling through a variety of websites as I usually do, and I came across an article which referenced this website called Qualys, where they have a tool called BrowserCheck. The site basically scans your web browser for vulnerabilities based on plugins which are installed.
Assuming you agree to the terms and conditions, it will install a plugin into your browser. Restart the browser and return to the site to run a scan. The tool will compare the versions of plugins/browser and then provide you with a list of issues.
Each issue links to the latest version (to the source) so you can manually update any components which are out of date. I thought I was relatively up-to-date as I regularly patch, and in fact most of my plugins were either up-to-date or a few minor revisions away from the current version.
If you patch/update even semi-frequently, it might be worth running this scan over your browsers at least once in a while, to avoid those pesky attack vectors.
Note: my largest vulnerability was Foxit PDF Reader, which was a major version out of date (v3 vs. v4) which should be a testament to how well the product works.