

Dirty Browser Enumeration Tricks – Using Chrome:// to Identify Firefox Plugins - mandatory
http://thehackerblog.com/dirty-browser-enumeration-tricks-using-chrome-and-about-to-detect-firefox-plugins/

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dpweb
<img src="about:logo" onload="alert('Browser is Firefox!')" />

Maybe this too?

<img src="about:logo" onerror="alert('Browser is NOT Firefox!')" />

