Question about sandbox

I’ve put Firefox sandboxed and I downloaded a new nVidia driver. Usually I have a Downloads folder for all that I download through Firefox.
All good, download complete then I went to Downloads folder and where’s my new downloaded driver? ;D
I found it in C:\Sandbox\firefox.exe\HarddiskVolume1\Downloads. :-TU
Copy/paste in my regular folder, installed all good.

My question is how/if I can define a folder outside the sandbox for downloaded files via Firefox sandboxed?