Quoting the support article:
Mozilla is ending official support for Firefox Price Tracker on September 30, 2019. An upcoming Price Tracker add-on update will notify active Firefox users of this retirement timeline. The Price Tracker add-on will also uninstall itself within approximately 30 days of this final update. Mozilla has no plans to resume Price Tracker in the future.
This is bittersweet for me as one of the developers of the experiment, but that is the nature of experiments!
If you would like to learn more, please refer to the support article linked above.