monline

To turn off file quarantine default behaviour (reboot required):
To disable quarantine for already downloaded files:
It's a great hint btw. Although I suggest if you disable file quarantine, you should also force Finder to always show file extensions (Finder Preferences / Advanced / Show all filename extensions). Otherwise you could launch a malicious app that disguises itself as a PDF (without the extension it's hard to tell what you're trying to launch).