Read all but write/modify new files only

[bobjohnson]

I was wondering if there is a way to allow a sandboxed application read access to a folder while allowing it to create new files but not allowing it to MODIFY any existing files?

The reason being i have firefox sandboxed and firefox and sandboxie are installed on an SSD but my download folder is on a mechanical drive (i download 1gb+ per day so i don't want to wear out my SSD too quickly). I want firefox to be able to bypass the sandbox for downloads to my downloads folder and be able to view current files in that folder (if i need to upload them) but not be able to overwrite or otherwise modify files which were there before the sandbox started (as the sandbox auto deletes when all applications exit).