From Mozilla Firefox Help

Add-ons are managed in the Add-ons manager. Select Tools > Add-ons to open it.
Updating Add-ons
By default, Firefox will periodically check when a new version for
one of your installed add-ons is available

If any are available, it will
prompt you at the next start to install any updates. You can change this
behavior in the Update tab
of the Advanced panel of OptionsPreferences.


You can check for updates manually by selecting the Extensions or
Themes panel and clicking the Find Updates button. If
updates are available, the Add-ons manager displays an Updates
panel, where you can choose the updates you want to install. Click the
Install Updates button to update those add-ons.
You need to restart Firefox for changes to take effect.


Disabling, Enabling, and Uninstalling Add-ons


If you want to get rid of an extension, you can either disable it temporarily,
so it is easily available should you want to enable it again in the future,
or uninstall it. Themes can only be uninstalled since all themes except the
current one are disabled automatically.



To disable or enable an extension, select the extension of your choice and
click its Disable or Enable button. To remove an add-on from
Firefox, select the add-on you wish to remove and click its
Uninstall button. You need to restart Firefox for changes to
take effect.


Further functionality


Further functionality such as Visit Home Page and About is
available by selecting the add-on of your choice, pressing
Ctrl and clicking onright-clicking the
add-on and selecting the respective item from the context menu.


Tasks specific to extensions or themes

Configuring Extensions


Extensions often provide a dialog to configure their functionality. To open
the optionspreferences dialog of an extension, select the Extensions panel, select
the extension of your choice, and click its OptionsPreferences button,
or simply double-click the extension.


Switching Themes


To switch between your installed themes, select the Themes panel, select the
theme of your choice, and click its Use Theme button. You need to
restart Firefox for changes to take effect.
of the Advanced panel of OptionsPreferences.