In the recent updates of Firefox, a service – Pocket (saves pages for reading later) was installed. You can either hide this functionality or disable it entirely.
To hide the Pocket plugin, navigate to the toolbar, right-click the Pocket icon and select Remove from Toolbar.
To unhide the Pocket plugin, navigate to the Open Menu icon on the toolbar and click on it, and click on Customise. Alternatively, you can right-click the toolbar and click on Customise. After reaching the Customise page, drag the desired icon backed onto the toolbar.
To disable the Pocket plugin, enter about:config in the address bar and acknowledge that you accept the risk. After this, type pocket.enabled into the about:config search bar, and then double-click the first (only) result so it changes from true to false. Exit the Firefox browser for changes to occur. The next time you you open the Firefox browser, the Pocket plugin will disappear.
To re-enable the Pocket plugin, follow the same steps as disabling the Pocket plugin, but instead double-clicking the first (only) result so that it changes from false to true. Remember to exit the browser for changes to occur.