"It shows the render as it works but when finished it is blank."

This rings a bell for me... In a previous version I had a similar problem with SuperFly, turned out the contrast in PostFX was set to -1 somehow(I didnt do it). Try unchecking 'apply post effects to render' and see if it makes a difference...

I have no idea why Firefly isn't working, but I suspect there may be a cross-bleed of settings that shouldn't happen... I've had renders in SuperFly that showed red splotches(like those that appear when calculating indirect light in Firefly) or incorrect Gama that seem to have been alleviated by turning off or adjusting settings in Firefly. Strange things sometimes surface in the unlikeliest circumstances, I think those are commonly referred to as 'bugs'.

Hope you find a solution...

Y'all have a great day.