Taking big moral stands on things like proprietary video codecs and DRM has never helped Mozilla do anything good for the web, unfortunately. Google just does what they want anyway. As long as this change in default search engine doesn't compromise the privacy of Firefox users (I don't think it does compared to how things were before?), they might as well take the money.

Then again, Yahoo's results always seemed rubbish so I immediately switched it to Google or Bing after installing...