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For example, Firefox has three sections for modifying the application:

  • Add-ons
  • Extensions
  • Plugins

They all seem to do the same thing: provide some extra functionality or disable existing functionality.

What are the main differences between them? How do you know that "what" you have is an add-on, an extension or a plugin?

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up vote 3 down vote accepted

Extensions and Plugins are different types of Add-on

Extensions add functionality to Firefox

Plugins allow Firefox to access additional media on the web (i.e. MP3 via QuickTime, SWF via Flash or PDF via Adobe Reader)

EDIT Further explanation following comment

There are actually three kinds of Add-on.

If you go to Tools -> Add-ons you will have 4 tabs including Extensions and Plugins, along with Themes and Get Add-ons.

Plugins are generally installed by other applications you have installed on your computer.

Extensions are generally installed in Firefox by the user.

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Bu ... if plugins and extensions are add-ons and FF provides a third option for add-ons, what are add-ons? – Tom Jun 25 '10 at 17:10
@Tom: FF provides an option to "get add-ons", which means, you can get both extensions and plugins via the same link. So Shevek's definition of add-ons is correct. – TFM Jun 25 '10 at 17:35

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