You may be in a situation where you need to upgrade your Joomla website, and you want to verify which extensions are being used to be sure they have an upgrade that works with the new version of Joomla.

Or it may be that your site has some conflict with an extension that is causing issues and you want to disable the extension or uninstall them.

Extensions can install Components and/or Plug-ins. They may do things on the Front End, the Administrative side or both. 3rd party extensions can be something as simple as a little plug-in that allows you to add your Google Analytics code to the <head> section or they can be a complex component that manipulates data from the database and pulls in multiple files from the core to create specific web pages and or do specific functions. Your site may depend on the extension for navigation, slideshows, page content organization, languages, comment sections, forms, any number of things. You need to be careful with disabling or uninstalling extensions.

The site may be 3 years old and you don't remember what extensions have been installed or you inherited a site from another developer and you weren't involved in all the development steps.

Looking for the 3rd party extensions installed on your site with Extension Manager

To see what has been installed, you can go into Extensions -> Extension Manager. Click on Manage from the list. In Extension Manager: Manage is a column labeled Author. If you see the name Joomla! Project, this is a core file. It came with the original Joomla installation. DO NOT REMOVE CORE FILES!!!

Some of the original files that came with Joomla, will not have Joomla! Project under Author. Some of these are the text editors of Code Mirror and TinyMCE.  Others are things like PHPMirror, phputf8, SimplePie, IDNA Convert, FOF The other things that come with the Joomla Installation are the included templates for the Front End and the Administrative interface. What all came with your original Joomla installation depends on what version you originally installed

3rd Party Extensions, those extensions that you installed from an outside source other than from joomla.org, will have an name in the Author list that is not Joomla! Project. If you do see an Author name other than Joomla! Project, that does not necessarily mean that it was not included with the installation, but it does give you your first clue that it is not a core file.

Other places to look for 3rd Party Extensions

Under Components

List of Joomla Core Components

Pull down the Components dropdown menu and look at the list of components.

The core installation of Joomla will have multiple components in this list, again depending on your original Joomla installation, these can vary.

If you see a component name other than the standard ones that came with the Joomla installation, these were put in there with 3rd Party Extensions.

The image to the left shows the Components that came with a Joomla 3.3 installation. Any thing that is not on this list, will likely be a 3rd Party component that was put there with an Extension.

These are not all of the Components with your Joomla installation. There is also a list of components under the Global Configuration menu.

Under Global Configuration

List of standard Joomla Components

Go to the Global Configuration page and you will see a list of the Components installed on your site. In this list are the standard components that come with Joomla and those installed by 3rd Party Extensions.

To the left is the list of the standard Components that came with a Joomla 3.3 installation.

Under Plugin Manager

Your 3rd Party Extension may have also installed Plug-ins that add functionality.

These would be in the list under Extensions -> Plug-in Manager.  Here is it not so easy to tell the difference between Plug-ins that came with the original installation or something that was installed with an extension.