Web Traffic Interception And Blocking

I've installed the Free Edition AV in my system. When trying to test the installation by downloading the EICAR test file I surprisingly had the page redirect to a page telling me that the website was blocked.


I'm using the Nightly builds of Mozilla Firefox. I cannot find any browser plugins installed neither my proxy settings were altered. So how does it work? It is important to know since it may interfere with testing the browser or make a browser bug surface. Thanks in advance.