Considering that Google search result ads are riddled with malware* and Google AdSense ads are riddled with malware and that Google Play has numerous ongoing issues with Android malware, I don't think it's really surprising that the Google Chrome Extensions store is also riddled with malware.
* Which my mother confirmed JUST THIS WEEKEND by searching Google for Firefox and Spider Solitaire clicking one of the Google ads up top for each to get the download and... 2 hours of cleaning later and removing 18 different malware apps. Then just deciding it was faster to restore it to a factory image.
* * Which I'm trying to block one by one using the pitiful tools that Google makes available to block individual adsense advertisers.
* Which my mother confirmed JUST THIS WEEKEND by searching Google for Firefox and Spider Solitaire clicking one of the Google ads up top for each to get the download and... 2 hours of cleaning later and removing 18 different malware apps. Then just deciding it was faster to restore it to a factory image.
* * Which I'm trying to block one by one using the pitiful tools that Google makes available to block individual adsense advertisers.