In light of the brouhaha over malware author acquisition of extensions for Chrome, a recent post by Martin Brinkmann at Ghacks might prove useful.

For FF it’s easy, and the extension, etc. are described in the article linked above.

For Chrome…not so easy. Chrome updates extensions automatically. So, you have to repeat the process in the article after each update. That’s a true PITA.

There is a second option: Add on Update Checker.

“Show a notification when an extension is updated.

Google Chrome Extensions are auto-updated. 
This is cool, no doubt about it, but how do you know when an extension is updated?

You don't until you install this extension.

▸ You will receive a notification when an extension is updated.
▸ If the updated extension has a log of records in its Chrome Web Store description, you can view it directly from the extension. 
▸ And unlike other extensions, it also works with disabled extensions.”

That will only tell you which have updated. Anyway…it’s the best I’ve found so far except for Chrome Protector.

There’s a new extension being offered: Chrome Protector (Chrome Shield) which will notify you if you’re running malicious extensions. 

“The new Chrome Protectorextension for Google Chrome has been created as a response of the recent news. It currently checks the installed extensions and will inform you if a malicious extension has been found.

How that is done? Currently by a blacklist.It is regularly updated based on user reports, the author's on research, and alerts posted on Reddit.” – Ghacks

Realize, though that this relies on people reporting problems after they’ve experienced them. It isn’t an “antiviral” giving active protection. It’s reputation based identifying extensions wich add malware sites, etc. as part of the acquired extension’s code.

For example, the report on my extensions (not all active/in use):

Hope this helps.