Hasn't ever done anything, but repeatedly reload background tabs. I am going to keep using tab suspender as long as I can even though it's getting deprecated for this one.

Edit: The last update seemed to get it working and now I can safely give it five stars as it is an improvement over the old addon. I just wish there was an option to keep a blank page there and only reload upon clicking that page rather than just unsuspending when the tab gets focus, but given that it actually seems to help firefox performance in too-many-tabs mode even more than the old per-quantum one did so I can live with it.