vidIQ for Firefox is not supported by versions of the browser older than 50.1.0. Therefore there is no guarantee that the extension will function as intended on older versions of the browser.
We strongly recommend that you upgrade to the most recent version of Firefox as new improvements and security patches are released on a regular basis.
Here is the official guide on how to install older versions of Firefox browser if you wish to do so:
Important: If you wish to use older version of Firefox without automatic updates (which is a default stetting in Firefox) you need to go to settings and change update options when you launch it for the first time.
List of known supported versions from newest to oldest:
Beginning from version 50.1.0 (12-Dec-2016) and newer
vidIQ can be installed and is functional
Versions 50.0 - 48.0
vidIQ can be installed from Firefox add-ons page but will not be functional
You can click the icon, but the appearing menu can't be seen and is inaccessible
Versions 47.0.2 - 0
vidIQ can't be installed