It was found that the FireFox setting called "Don't Remember History" actually puts FireFox into a private browsing mode or what Chrome calls Incognito mode.
In this mode communication with extensions is disabled and thus we can not check the version of the extension.
More information can be found here : https://support.mozilla.org/en-US/kb/private-browsing-control-what-info-firefox-saves?redirectlocale=en-US&redirectslug=Private+Browsing