Adblock plus is a content-filtering extension for iceweasel, firefox, seamonkey, and several other applications; it allows users to prevent webpage elements, such as advertisements, from being downloaded and displayed.

on the first run, adblock plus will ask you if you want to subscribe to a filter list, which is automatically updated and blocks a lot of common advertisements. additional filters can be added at will, and it's also possible to use wildcards in order to block e.g. all images or javascript files from specific servers or directories.