manifest.json

{
"update_url": "https://clients2.google.com/service/update2/crx",

    "name" : "edX & XueTangX Subtitle Download", 
    "version" : "0.6.1",
    "manifest_version" : 2,
    "content_scripts" : [
        {
            "matches" : [
                "https://futurelearn.com/*",
                "https://www.futurelearn.com/*", 
                "https://courses.edx.org/courses/*", 
                "http://www.xuetangx.com/courses/*", 
                "http://xuetangx.com/courses/*", 
                "https://class.coursera.org/*"
            ], 
            "js"      : ["jquery-2.0.3.min.js", "main.js"], 
            "run_at"  : "document_end"
        }
    ], 
    "icons": {
        "16": "icons/16.png",
        "32": "icons/32.png",
        "48": "icons/48.png",
        "64": "icons/64.png",
        "128": "icons/128.png"
    }
}