You still need an anti-virus program and a firewall. Firefox is just a web browser.

Thanks for the clarification.

Unless you are in love with Kaspersky, why not consider using a free (for personal use) anti-virus application that doesn't install unnecessary (IMHO) extensions that muck-up Firefox, which may not be updated in a timely manner when a new version of Firefox comes out.

Avira Personal Free - http://www.free-av.com/

How would I deactivate Kaspersky and install Avira Personnal?

Uninstall Kaspersky thru the Windows Control Panel and then install Avira.

Would you rate Avira over AVG?