Know what you are doing. Rated 1 out of 5 stars

Pay attention. AdBan is a resolver proxy. You will be submitting every URL you try to access to them for scrutiny. But also data logging and mining. They want to make money. You may or may not care, but you should be aware of this.

This review is for a previous version of the add-on (1.5.1). 

AdBan doesn't submit every URL you try to access.
AdBan submits truncated URL to the server only when the corresponding locally cached ad filter becomes stale. Since typical ad filter usually covers many sites simultaneously and currently cached ad filters become stale in 48 hours, AdBan sends only a small fraction of truncated URLs you visit to the server. Read more detailed explanation of ad filters' update mechanism employed by AdBan at https://addons.mozilla.org/en-US/firefox/addon/adban/reviews/269999/ .
Since AdBan's source code is open, you can investigate it at http://code.google.com/p/ad-ban-extensions/source/browse/ if you don't trust the explanation given above.