References:

• Content Scripts


• Manifest File

You can take the following code as a reference for adding some HTML Code.

manifest.json

This file registers content script to extension.

{

name:Inject DOM,

description:http://stackoverflow.com/questions/14068879,

version:1,

manifest_version:2,

content_scripts: [

    {

      matches: [http://www.google.co.in/*,https://www.google.co.in/*],

      js: [myscript.js]

    }

  ]

}

myscript.js

A trivial script for adding a button to Google page

// Checking page title

if (document.title.indexOf(Google) != -1) {

    //Creating Elements

    var btn = document.createElement(BUTTON)

    var t = document.createTextNode(CLICK ME);

    btn.appendChild(t);

    //Appending to DOM 

    document.body.appendChild(btn);

}

Output

You see a button added to a desired page