Browser extension development allows developers to add functionality to the browser and enhance the user interface in a way that is not directly related to the viewable content of Web pages. This class of extensibility includes add-on functionality that users might install to enhance their browsing experience.

Browser Extension Development includes the following:

• Shortcut menu extensions: It is possible to extend your browser by adding options to the shortcut menu. Adding registry key that link to the menu command can help accomplish this task. A shortcut menu extension forms part of Firefox extension development and even IE extension development.
• Toolbars: Toolbar development helps users to access multiple applications without navigating away. It makes it simple for the user to gain one click access to news, networking site, emails alerts, bookmarks, and so on.
• Explorer Bars: IE extension development includes IE explorer bars such as search bar, favorite bar, history bar, and channels bar. These explorer bars can be enabled or displayed as per user’s choice. When you enable the Explorer bar, a left pane and right pane are displayed in the Internet Explorer window. If you select the Favorites, History, or Channel bar, the contents of your Favorites, History, or Channels folder are displayed in the left pane. Firefox extension development also includes Explorer bars.
• Browser Helper Objects. A Browser Helper Object (BHO) is made as Firefox extension development and IE extension development and runs within your browser and offers additional services, often without any obvious user interface. It is a DLL module designed as a plugin to provide added functionality. Most BHOs are loaded once by each new instance of your browser.