It doesn't work in simplest scenario. Like,

I type the url in the address box, say www.linkedin.com
Browser tries to establish connection and timouts.
I press add-on's button with "X" on it.
I see nice box with "Non-proxied page" on it and nice picture like My Computer -> about:newtab.
I see www.linkedin.com in the address box.
I stay puzzled about how the hell do I enable this add-on for this site.

I do not consider this scenario like anything near to "working". Do developers ever test their products these days?