After installing Pocket for Firefox, a toolbar button will appear in Firefox's Navigation Toolbar. If you cannot find this button, please make sure that the Navigation Toolbar is visible, and that the button has been added correctly
Enabling the Navigation Toolbar
In order to verify that your Navigation Toolbar is showing, please go to View menu, select Toolbars, and make sure that the Navigation Toolbar is checked.
Customizing the Toolbar
To add or rearrange the Pocket toolbar button in the Navigation Toolbar, right-click on the toolbar and select Customize, or go to View > Toolbars > Customize. A window will appear which allows you to edit the toolbar buttons via drag and drop. Find the button called "Reading List", and drag it to your desired location.