This is a new development. Happening on all of my Mac OSX machines. Whenever I download a file from Firefox, the downloaded file now has write permissions set for group and other: -rw-rw-rw- instead of the more reasonable read-only permissions for group and other: -rw-r--r-- This is a new development: all of my downloads started displaying these fully writable permissions about a month ago. Happening on multiple computers, so this is tied to Firefox v77.