There are often multiple things that your anti-virus installs on your computer. One is the actual anti-virus, which is always running, regardless of what browser you are using or what you are doing. Another thing is a browser extension, which is injected into your browser. The anti-virus company says it makes you safer, but it actually just duplicates protection your browser already has and is usually just used to gather data about you. You likely just lost the extension, your anti-virus itself is still running. You are running Windows 10, so I'd actually STRONGLY suggest you remove f-secure entirely from your computer, and just use the built in Windows Defender that comes with Windows 10, and then install Malwarebytes (www.malwarebytes.com) and run scans once a month with that. This solution is free, and will keep you safer and give you a better performing computer. Of course, make sure to keep Windows and Firefox up to date.