Sorry, but the statusbar/addonbar is missing in new versions of Firefox.
The current version of Forecastfox is the version for the new API: WebExtensions

But I'm not guilty - 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/

But do not worry, I'll come up with a workaround and will return Forecastfox previous form