title: How to set proxy settings in firefox addons?
body: <p>I need to set a proxy setting, when the addons installed. I follow documentations here <a href="https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/API/proxy/settings" rel="nofollow noreferrer">https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/API/proxy/settings</a>. But, its not worked.</p>
  
  <p>Manifest</p>
  
  <pre><code>{
    "manifest_version": 2,
    "name": "Secure Proxy",
    "version": "1.0",
  
    "description": "Secure Proxy.",
  
    "permissions": [
      "proxy"
    ],
  
    "background": {
      "scripts" : ["js/background.js"]
    }
  }
  </code></pre>
  
  <p>background.js</p>
  
  <pre><code>let proxySettings = {
    proxyType: "manual",
    http: "118.97.151.130:9090",
    httpProxyAll: true
  };
  
  browser.proxy.settings.set({value: proxySettings});
  </code></pre>