Installed Magento CE 1.6/7/8/9 + sample datas on my dev server
when editing a product in back office, in "custom options" tab, "+ add new option" does not do anything and no JS error logged...
did not find solution in official Magento forums (currently under maintenance)
tried to read official doc about custom options but Google + Magento doc internal search module (I guess it uses Google too) sends me too doc home page, can't access indexed pages.