JSTOR uses OpenSearch (there is a <link rel="search"> on their pages). This gives browsers information about their search engine. If you look through the list

JSTOR uses OpenSearch (there is a <link rel="search"> on their pages). This gives browsers information about their search engine. If you look through the list of search engines that got automatically added to Chrome, you'll notice that some of those sites to not have the autodiscovery link. Chrome will try to autodetect search engines (probably by looking for a form field named "search"), but this doesn't always work.