Instead of removing just the uls-preferences key, you bring down everything, including data stored by other extensions (namely Popups).
Steps to reproduce:
- Open a private window (to make sure there are no cookies) and vgo to https://el.wikipedia.org/ (because this wiki has HoverCards enabled by default).
- Hover an article link and click the gear icon inside the popup.
- Select the second option (Απενεργοποίηση προεπισκόπησης, that's greek for Disable preview) and click Αοιθήκευση (Save).
- At this point you are presented with instructiona how to enable preview again, and it is the right time to open the web console of your browser and type $.jStorage.get("mwe-popups-enabled") and verify that the preference is saved as false
- Press Εντάξει (greek for OK), the page realoads and now $.jStorage.get("mwe-popups-enabled") returns null Also try localStorage.jStorage to verify that the complete store is wiped.
- Hover an article link. A popup appears although it was disabled.