The statusbar/addonbar is missing in new versions of Firefox.
The current version of Forecastfox is the version for the new API: WebExtensions (supported Firefox and Google Chrome)

WebExtensions not supported "statusbar/addonbar" from xul-addons like as "Addon-bar restored", "Status-4-ever" , etc

These are the inevitable changes in Firefox - all Xul-addons is die in Firefox 57 (November 2017)
https://blog.mozilla.org/addons/2017/02/16/the-road-to-firefox-57-compatibility-milestones/