To view the list of installed plugins (also known as add-ons) in Firefox:
Open Firefox.
Click the menu button (the three horizontal lines in the top-right corner of the window) and select "Add-ons" from the menu.
The Add-ons Manager tab will open. On the left side of the tab, you'll see a list of categories. Click the "Plugins" category.
The right side of the tab will display a list of all installed plugins. You can disable or remove a plugin by clicking the corresponding button next to it.
To see more information about a plugin, click on its name. This will open a new window with details about the plugin, including its version number and publisher.
Alternatively, you can also type "about:addons" (without the quotes) in the address bar and press Enter to go directly to the Add-ons Manager.