Safari: Mac asks for more and more Space for Firefly

Hi,

I played quite a bit with Firefly. I use it in Safari on an Mac Mini. Even thou I used it in several sessions it keeps asking for more and more space an my mac. It seems to accumulate all the sessions. Now it already asks if Firefly can use 6gb on my mac.

Is there someway to stop it or reset that? What is it saving there?