navigator.platform returned "Win32" while navigator.userAgent said Linux when
using the stealth client. page.rs now calls set_platform("Linux x86_64", "Linux", "")
alongside set_user_agent when the stealth client is active.
bootstrap.js: pre-declare 71 internal _* globals as enumerable:false before
var runs, so they don't show up in Object.keys(window) on real pages.