it seems that there may be something wrong in the way FF uses the selections load, because is right that you can put the selection input
only as an option, and even you can put a checkbox to disable it so is clearly optional, but seems that it does not care, it will always require a selection, or at least, always will be shown the message
And I think that it is in middle and center of screen so you surely see it and know that you have to load a selection
One way
if the selection is optional and not an essential and required part of the filter, is to enter inside the filter and switch it off, I mean disconnect the selection or delete it, so this surely removes the warning message