Privacy Badger automatically blocks spying ads and invisible trackers as you browse. It’s there to ensure that companies can’t track your browsing without your consent.
Here are a few details from the developer of the script:
Privacy Badger sends the Do Not Track header with each request and evaluates the likelihood that you are still being tracked. If a domain appears to be tracking you on multiple websites, Privacy Badger automatically blocks your request from being sent to the tracking domain. Please understand that Privacy Badger is in alpha, and the algorithm’s determination is not conclusive that the domain is tracking you.
Our extension shows you one of three states for each tracker. Red means block the tracker. Yellow means that we don’t send cookies or referers to the tracker. Green means unblocked (probably because the third party does not appear to be tracking you – yet). You can click on the Privacy Badger icon in your browser’s toolbar if you wish to override the automatic blocking settings.
You can grab the Privacy Badger from the Firefox Add-ons website.