Mozilla Firefox has a built-in virus scanner.. If you have already installed an antivirus software on your computer, you can disable the Firefox scanner. Thus, double-scan can be avoided. To disable this feature:
- In the address bar type the following command : about:config
- Click on the: "I'll be careful, I'll promise" button.
- Search for the following entry: browser.download.manager.scanWhenDone
- Toggle its value to "False"