Extension Defender is a simple browser add-on which can scan your PC for potentially unwanted extensions (adware, spyware or malware). Once running it checks other extensions before they're installed, warning you of any problems.
Extension Defender is, well, rather basic. It offers two sections, "Scan" and "Options". Click the second and you're told "theres currently no options to set". The first has only a "Scan" button, and clicking this returns its results in a second or two.
Anything dubious will be listed in a simple report. A "Remove" button uninstalls the extension right away, and a "Rescan" option should confirm your system is clear".
A notification badge on the extension icon also displays the number of malicious extensions you've installed. And signatures are updated automatically, so once installed you don't have to manage Extension Defender any further.