Hello, thank you.
Yes, because of a few limitations in the Firefox API, this is creating in fact a small browser window, not a simple property panel, so this is is slower. And to add to that, some Firefox discrepancies between OS and behavior force an opening in two steps, creating the window very small and at default place, and then moving it and enlarging it to get it painted properly :-(

Now, on the position of the window itself, it is saved, so you can move it, and next time it is open, it will reappear at the place you moved it to the previous time, so that should solve your point about not seeing the input folder name field (note: that also works if you have firefox spanning multiple screens ..)