Searchonymous helps to prevent your Google searches from tracking by Google or the NSA. When installed no tracking cookies are sent to Google while searching. This is done by blocking certain Google cookies (such as the PREF-ID) or generating randomized ones (which are worthless for tracking).
Here is more information about the script from the developers:
Other cookies that just contain your search preferences will be allowed, so your preferences are preserved. You will stay logged in on other Google services such as Youtube or Gmail. It also removes ads and clutter from the Google main page that is normally shown when cookies are disabled.
Want to check this add-on out? You can pick up Searchonymous at the Firefox Add-on website.