title: How to add a button to enable background script?
body: <p>I have a background.js file which can intercept the web requests and replace the value of <code>User-Agent</code> header. It works fine as per the below manifest. </p>
  
  <pre><code>{
    "manifest_version": 2,
  
    "name": "TamperHeaders",
    "description": "Replace HTTP headers and parameters",
    "version": "1.0",
  
    "browser_action": {
      "default_icon": "38.png"
    },
  
    "background": {
      "scripts": ["background.js"]
    },
    "permissions": [
      "webRequest",
      "webRequestBlocking",
      "&lt;all_urls&gt;"
    ]
  }
  </code></pre>
  
  <p>I want to add a <code>default_popup</code> and add a button to that popup, say "Click me!", and upon clicking on the button, the extension should get activated (i.e.,the background.js should start to run). How can I achieve this?</p>