It looks like it really isn't an add-on, but instead a stand-alone program. [I'm putting this post here in Add-ons because I'm curious to find out if AdFender works in the same way as Adblock Edge / Adblock Plus.] In doing research on AdFender's website, I noticed this in a Q&A section:
Is this the same way Adblock Edge / Adblock Plus, etc., works? I must admit that after reading this, I am leery of installing AdFender. Can someone educate me on this?AdFender runs as a HTTP proxy server on your local computer. It does not depend on our servers for browsing the Internet.
After AdFender is installed or updated, your security software must be configured to allow AdFender to connect to the Internet. When your browser tries to connect to a web server, it is instead connected to the local AdFender program and AdFender connects to the web server on behalf of the browser. When the firewall notifies you that AdFender is trying to connect to the Internet or act as a server, you MUST allow access, for AdFender to work properly.
In addition, it seems like you'd have to either start it up manually, or have it configured to start upon system boot-up, since it's a stand-alone program. Either way it is a minus (extra click or draining resources when not needed).