Firefox and Thunderbird plugins for free software habits

Description of the project: there are already several plugins for helping people think twice about visiting web sites they want to avoid. Let's take this concept further by helping people avoid non-free sites and recommending free alternatives. The plugins need to recognize non-free sites (for example, Doodle or Meetup) when they appear in the browser or in an email and encourage the user to use an alternative (for example, Framadate instead of Doodle). See this blog post for some initial ideas and suggested reading. Some ideas are also mentioned in this discussion thread