This can affect JavaScript-based tracking of browser statistics.[7] While most browsers generate additional page hits by refreshing web pages when the user navigates back through page history, some browsers (such as Opera) reuse cached content without resending requests to the server.[8][9] Generally, the more faithfully a browser implements HTTP's cache specifications, the more it will be under-reported relative to browsers that implement those specifications poorly.[9] Browser users may run site, cookie and JavaScript blockers which cause those users to be under-counted. For example, common AdBlock blocklists such as EasyBlock include sites such as StatCounter in their privacy lists, and NoScript blocks all JavaScript by default. addons.mozilla.org reports 15.0 million users of AdBlock variants and 2.2 million users of NoScript. Users behind a caching proxy (e.g. Squid) may have repeat requests for certain pages served to the browser from the cache, rather than retrieving it again from the Internet.