The original status bar (add-on bar) was removed from Firefox in version 29 (May, 2014) and all existing addons that emulate that bar are coded using XUL.
https://www.mozilla.org/en-US/firefox/29.0.1/releasenotes/

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

And 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/

So forget about the xul-version, there are a few months left before the complete destruction of all the old add-ons...