What is the difference between a Firefox extension and a Firefox add-on?

Question

The terms "extension" and "add-on" seem interchangeable, but I have seen instances where people seem to mean different things with "extension" vs "add-on."

Clarity please?

Answer 1

Here is a quote from Firefox add-ons FAQ:

What are the different types of add-ons?

There are several kinds of add-ons that customize Firefox in different ways:

• Extensions add new features to Firefox or modify existing functionality. There are extensions that allow you to block advertisements, download videos from websites, integrate more closely with social websites, and add features you see in other applications.
• Complete Themes change the entire appearance of Firefox, usually including icons, colors, dialogs, and other visual styles.
• Themes are lightweight themes that use background images to customize your Firefox toolbars.
• Search Providers add additional choices to the search box dropdown. These providers allow you to quickly search any website.
• Dictionaries & Language Packs add support for additional languages to Firefox.
• Plugins help Firefox display or understand different types of media, such as Adobe Flash or Apple Quicktime.

Answer 2

Found the best answer on this page:

https://addons.mozilla.org/en-US/developers/docs/sdk/latest/dev-guide/guides/sdk-vs-xul.html

An Add-on is a sandboxed package that uses an SDK designed for writing Add-ons.

A XUL extension is not sandboxed and has full access to the internals of Firefox (and all of the complexity that comes with it).

The Add-on SDK is here: https://addons.mozilla.org/en-US/developers/docs/sdk/latest/

The XUL documentation home is here: https://developer.mozilla.org/en-US/docs/XUL

Answer 3

Extensions and Plug-ins are both types of Add-ons which is the umbrella term. I think the difference between them is that Extensions tend to add new functionality whereas Plug-ins tend to modify existing behaviour but there does seem to be an overlap.

Answer 4

Add-on is an inclusive term for a category of augmentation modules that are subdivided into plugins, themes, search engines, extensions, snap-ins, or various other vendor-specific names.

• A plugin (plug-in, addin, add-in, addon or add-on) is a computer program that interacts with a main (or host) application (a web browser or an email program, for example) to provide a certain, usually very specific, function on demand.

• In computing, a patch is a small piece of software designed to update or fix problems with a computer program or its supporting data. This includes fixing bugs, replacing graphics and improving the usability or performance.

• In computing, skins and themes are custom graphical appearances (GUIs) that can be applied to certain software and websites in order to suit the different tastes of different users.

Answer 5

Addons and extensions are the same, it's a whole that includes themes aswell.

The different part here are the plugins, that help your browser perform specific functions like viewing special graphic formats or playing multimedia files such as the adobe reader, flash, silverlight, quicktime etc.

Plugins are slightly different from extensions, which modify or add to existing functionality.

In fact in the browser itself it uses both terms interchangeably "Get Add-ons" but once installed they reside under the "Extensions" tab.

Answer 6

In this context, extensions are a subset of addons.

So addons are an umbrella term for extensions, themes, dictionaries etc.

Answer 7

Add-ons are installable enhancements to the Mozilla Foundation's projects (and compatible variants such as Portable Firefox). Add-ons allow the user to add or augment application features, use themes to his or her liking, and handle new types of content.

Extensions can be used to modify the behavior of existing features to the application or add entirely new features. Extensions are especially popular with Firefox, because Mozilla developers intend for the browser to be a fairly minimalistic application in order to reduce software bloat and bugs, while retaining a high degree of extensibility, so that individual users can add the features that they prefer.

Reading Add-on (Mozilla) may help

Answer 8

Add-on refers to both extensions and themes, Firefox 3 (IIRC) moved both themes and extensions to a single menu item.