Q:

Chrome extension Script Injection to each open tab

I tried to build simple extension according to the examples: 
from here  and here
and I must be doing something wrong here.
All I want is for start that on each loading page ( or even better before loading ) it will popup 
hello alert
manifest.json
{
   "background": {
      "page": "background.html"
   },
   "content_scripts": [
    {
      "matches": ["http://*/*","https://*/*"],       
      "js": ["jquery-1.8.2.min.js","contentscript.js"],
      "run_at": "document_end"
    }
   ],
   "web_accessible_resources": [
    "script_inpage.js"
   ],
   "browser_action": {

      "default_popup": "popup.html",
      "default_title": "Test 123"
   },
   "content_security_policy": "script-src 'self'; media-src *; object-src 'self'",
   "description": "Simple Test 123.",

   "manifest_version": 2,
   "minimum_chrome_version": "18",
   "name": "Test 123",
   "permissions": [ 
        "unlimitedStorage",
        "http://*/",
        "tabs",
   ],

   "version": "2.6"
}

background.html is empty for now 
contentscript.js:
var s = document.createElement('script');
s.src = chrome.extension.getURL('script_inpage.js');
(document.head||document.documentElement).appendChild(s);
s.onload = function() {
    s.parentNode.removeChild(s);
};

script_inpage.js:
alert("this is script");

There is no error even when I trigger the developer console window. 

A:

Your manifest file is invalid, there's a superfluous comma after the last entry in the "permissions" section:
"permissions": [ 
    "unlimitedStorage",
    "http://*/",
    "tabs", // <-- Remove that comma
],

If you want your script to run as early as possible, use "run_at": "document_start" instead of "document_end". Then, your script will run before <head> and <body> even exist.

