Maybe you don't download risky files, maybe you have an anti-virus program that just repeats the scan. You'll want to turn this feature off.
- Click the address bar at the top, which is called Awesome Bar by Mozilla.
- Type in 'about:config'.
- Click 'Okay' for the warning. Don't mind it.
- In the search bar at the top of this page, type in 'browser.download.manager.scanWhenDone'.
- When it appears in the results, double-click it to switch the value from true to false.