Unfortunately it looks like running the browser in the sandbox with Run Safer can actually interfere with the virtualization. I downloaded a file with the “Save downloads to outside sandbox” not checked, and the file was saved outside the sandbox anyway. So if you use Run Safer, might be better to run the browser outside the sandbox and then go to Explorer and click on “run in sandbox” for the downloaded file. Don’t know what other interference it might cause or if there are offsetting benefits of running them together.