That sounds like it might be the ASK toolbar. You should be able to remove that using the control panel Programs & Features. The ASK toolbar is annoying but shouldn't prevent you from adding extensions as far as I know.I notice that when I checked my extension page I wouldn't find Google Cast or any of the other extensions I added in the last hour. However I did find an extension call "Ask." I had this app remove in the trash bin, but when I reopened the page, it was right page back on the extension page.