"The http://addons.mozilla.org website, hosted on Mozilla servers, offers many addons to extend FireFox with additional features. The majority of these addons are not developed directly by Mozilla but by third party developers. Many of these addons don't explicitly define a license, even if the original author thought it was unnecessary, so they can't be considered Free Software. Because of this issue, the GNU IceCat browser can't advise users to install and use them, in general. Below is the list of addons that we have checked to be Free..."