There is a new "Setup Efficy Sidebar and Add-ins 10SP2 Plus r14440" msi package available on the Partner FTP which addresses a Firefox-related certificate issue in the Sidebar.
Since Firefox 59+ for new installations there was no installation of the Root CA certificate because of a format change in the certificate DB of Firefox. Without certificate Firefox would not communicate correctly with the local web server running in the Sidebar.
The new Setup takes into account this change of format. If your customers don't use Firefox, the new Setup won't change anything.