browser_action

Type Object
Mandatory No
Example
"browser_action": {
  "browser_style": true,
  "default_icon": {
    "16": "button/geo-16.png",
    "32": "button/geo-32.png"
  },
  "default_title": "Whereami?",
  "default_popup": "popup/geo.html"
}

A browser action is a button that your extension adds to the browser's toolbar. The button has an icon, and may optionally have a popup whose content is specified using HTML, CSS, and JavaScript.

If you supply a popup, then the popup is opened when the user clicks the button, and your JavaScript running in the popup can handle the user's interaction with it. If you don't supply a popup, then a click event is dispatched to your extension's background scripts when the user clicks the button.

You can also create and manipulate browser actions programmatically using the browserAction API.

Syntax

The browser_action key is an object that may have any of the following properties, all optional:

Name Type Description
browser_style Boolean
New in Firefox 48

Optional, defaulting to false.

Use this to include a stylesheet in your popup that will make it look consistent with the browser's UI and with other add-ons that use the browser_style property. Although this key defaults to false, it's recommended that you include it and set it to true.

In Firefox, the stylesheet can be seen at chrome://browser/content/extension.css, or chrome://browser/content/extension-mac.css on OS X.

The Firefox Style Guide describes the classes you can apply to elements in the popup in order to get particular styles.

The latest-download example add-on uses browser_style in its popup.

default_icon Object or String

Use this to specify one or more icons for the browser action. The icon is shown in the browser toolbar.

Icons are specified as URLs relative to the manifest.json file itself.

You can specify a single icon file by supplying a string here:

"default_icon": "path/to/geo.svg"

To specify multiple icons in different sizes, specify an object here. The name of each property is the icon's height in pixels, and must be convertible to an integer. The value is the URL. For example:

    "default_icon": {
      "16": "path/to/geo-16.png",
      "32": "path/to/geo-32.png"
    }

See Choosing icon sizes for more guidance on this.

default_popup String

The path to an HTML file containing the specification of the popup.

The HTML file may include CSS and JavaScript files using <link> and <script> elements, just like a normal web page.

Unlike a normal web page, JavaScript running in the popup can access all the WebExtension APIs (subject, of course, to the extension having the appropriate permissions).

default_title String

Tooltip for the button, displayed when the user moves their mouse over it.

This is a localizable property.

Choosing icon sizes

The browser action's icon may need to be displayed in different sizes in different contexts:

  • The icon is displayed by default in the browser toolbar, but the user can move it into the browser's menu panel (the panel that opens when the user clicks the "hamburger" icon). The icon in the toolbar is smaller than the icon in the menu panel.
  • On a high-density display like a Retina screen, icons needs to be twice as big.

If the browser can't find an icon of the right size in a given situation, it will pick the best match and scale it. Scaling may make the icon appear blurry, so it's important to choose icon sizes carefully.

There are two main approaches to this. You can supply a single icon as an SVG file, and it will be scaled correctly:

"default_icon": "path/to/geo.svg"

Alternatively, you can supply several icons in different sizes, and the browser will pick the best match.

In Firefox:

So you can specify icons that match exactly, on both normal and Retina displays, by supplying three icon files, and specifying them like this:

    "default_icon": {
      "16": "path/to/geo-16.png",
      "32": "path/to/geo-32.png",
      "64": "path/to/geo-64.png"
    }

In Chrome, the default height and width is 19 * window.devicePixelRatio. So to get an exact match on Firefox and Chrome, Retina and non-Retina:

    "default_icon": {
      "16": "path/to/geo-16.png",
      "19": "path/to/geo-19.png",
      "32": "path/to/geo-32.png",
      "38": "path/to/geo-38.png",
      "64": "path/to/geo-64.png"
    }

If Firefox can't find an exact match for the size it wants, then it will pick the smallest icon specified that's bigger than the ideal size. If all icons are smaller than the ideal size, it will pick the biggest icon specified.

Chrome incompatibilities

None.

Example

"browser_action": {
  "default_icon": {
    "16": "button/geo-16.png",
    "32": "button/geo-32.png"
  }
}

A browser action with just an icon, specified in 2 different sizes. The extension's background scripts can receive click events when the user clicks the icon using code like this:

 browser.browserAction.onClicked.addListener(handleClick);
"browser_action": {
  "default_icon": {
    "16": "button/geo-16.png",
    "32": "button/geo-32.png"
  },
  "default_title": "Whereami?",
  "default_popup": "popup/geo.html"
}

A browser action with an icon, a title, and a popup. The popup will be shown when the user clicks the button.

For a simple, but complete, extension that uses a browser action, see the walkthrough tutorial.

Document Tags and Contributors

 Contributors to this page: wbamberg, Makyen, hansifer, fmarier, LonM
 Last updated by: wbamberg,