After selecting Options>Personization and installing a Firefox persona - if you select the Revert button - Nothing happens. The persona recently installed is not uninstalled. I would recommend this button be programmed so that it would either re-install the previous persona installed - or if no previous persona existed, it would default to "Plain look."
*** This bug has been marked as a duplicate of bug 58132 ***
It would be great if this button could be set up to either restore the last persona that was installed or, in the absence of https://space-barclicker.com such, to automatically select "Plain look."