We don't log searches in an identifiable way.  Prior to the release of the add-on we added some extra text to our privacy policy (found here: http://www.trueknowledge.com/privacy/ ) to spell out how we use search terms that are transmitted to True Knowledge via the add-on.

Here is a quote from our privacy policy: "All use of the add-on is anonymous, we do not associate any personally identifiable information with the information transmitted to our servers via the add-on."

We take privacy very seriously so if you have any more concerns please let us know.

As for enabling and disabling the add-on without restarting Firefox...I imagine this would be possible, although I have never come accross any add-ons that has this feature...I'll have a think about this.

Thanks nick, that's very helpful and I'm glad to hear that privacy is taken seriously, particularly with everyone's google searches. 

I think whether or not it's common to be able to turn it off, it's advantageous to be able to do so, though you don't have to make it too easy to turn off and you can still make it easy to turn back on.  I'm actually more interested in the latter as I found once I'd disabled it from firefox addons temporarily I was less inclined to turn it back on and have to restart.