Scriptable background HTTP(s) client with cookie handling

A solution is required that will allow for automation on the client side and reduce changes required on a legacy business management system. Goal is to create a background application that can make identical web requests (GET, POST) to a browser, with full cookie and header management. Cookies should be able to be loaded using cookies found in other installed browsers. Application should be scriptable using JavaScript The application should be able -Make web requests to any website a browser can reasonable access, perfectly emulating the use of headers and cookies -Run in the background without user intervention -Download commands in the form of JavaScript from the central server to be run on start-up with polling for updates every x minutes -Detect and load the cookies from the cookie store of Firefox, Chrome, Safari -Be partially script-able so as to allow a basic JavaScript to command and process the web-requests -Run on Windows 8, 7, XP depending on complexity, main target is windows 7 -Have basic update system to poll and retrieve updates from the central server