User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:57.0) Gecko/20100101 Firefox/57.0 Build ID: 20170823100553 Steps to reproduce: Using Nightly (2017-08-23) the download icon is not available within the customise menu and cannot be placed onto the toolbar. This seems to be the default behaviour when using this version of nightly. Actual results: The Download arrow icon is not visible and cannot be added to the toolbar, even when something is downloaded. Expected results: The icon should appear within the customise menu and be fully customizable.