Firefox Add-ons Workshop

CMRIT | 29th July, 2017

Santosh Viswanatham

Work at Infosys Ltd

Mozilla Tech Speaker

Mozilla Rep

Web Developer

@isantoshv | |


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A global Community of Volunteers

  • Browser Add-ons
  • WebExtensions
  • Anatomy of WebExtensions
  • Building your first Add-on


Browser Add-ons extend and modify the functionality of the browser.

Browser Add-ons?

Firefox is the most customizable browser!

1 Million+ addons downloaded everyday

70+ Add-ons published everyday

250 million+ Add-ons used everyday

2000+ users signup everyday


A cross-browser system for developing browser add-ons

  • Uses standard HTML, CSS and JS
  • e10s compatible (multiprocess)
  • Few changes and you can run it on Chrome, Edge and Opera
  • Documentations from multiple resources.

Why WebExtensions?

Few WebExtension API's

Anatomy/Architecture of WebExtensions


  "manifest_version": 2,
  "name": "inShorts in dark",
  "version": "2.0.1",
  "homepage_url": "",
  "description": "Read your favourite news on inShorts by dimming the light right away on your browser.",
  "icons": {
    "48": "icons/icon-48.png",
    "96": "icons/icon-96.png"
  "permissions": [
  "browser_action": {
  "browser_style": true,
  "default_icon": {
    "19": "icons/icon-19.png",
    "38": "icons/icon-38.png"
  "default_title": "Turn on or off"
  "background": {
    "scripts": ["background.js"]

Background scripts

  • Loaded as soon as the extension is loaded

  • Stay loaded until the extension is disabled or uninstalled

  • You can use any of the WebExtension APIs in the script

"background": {
  "scripts": ["background-script.js"]

Content Scripts

  • Similar to loading normal scripts in the page

  • Can access DOM structure and use a small subset of the WebExtension APIs

  • Make cross-domain XHR requests

  • Exchange messages with their background scripts and can in this way indirectly access all the WebExtension APIs

"content_scripts": [
    "matches": ["*://**"],
    "js": ["jquery.js", "content-script.js"]

Browser action

  • Used to add button to browser toolbar
  • Use this when your add-on's features are applicable to all websites else use Page action instead.
"browser_action": {
  "default_icon": {
    "19": "button/geo-19.png",
    "38": "button/geo-38.png"
  "default_title": "Whereami?",
  "default_popup": "popup/choose_beast.html"

Page action

  • Used to add button to address toolbar
  • Use this when your add-on's features are specific to a particular website.
"page_action": {
  "default_icon": {
    "19": "button/geo-19.png",
    "38": "button/geo-38.png"
  "default_title": "Whereami?",
  "default_popup": "popup/choose_beast.html"

Resources such as images, HTML, CSS, and JavaScript that you include in the extension.

Developing your first browser add-on

  • Adding a browser action
  • Adding a page action
  • Accessing DOM from content scripts
  • Using a couple of WebExtension API's
  • Debugging your add-on

Debugging your add-on



Need help?

IRC Channels: #webextensions, #extdev, #addons

Mailing List:

Telegram: @addonschat


Santosh Viswanatham | @isantoshv |