Saving Forests by Surfing the Net???

Could this be a way to save forests without even getting out of your pajamas? Check this out: if you use the new search-engine, ecosia, they claim that they donate 80% of their profits to the World Wildlife Fund (WWF) – but wait, there’s more! They also promise to save 2 square meters of rainforest for each of our searches. Apparently, over 150 million square meters saved so far. How does this work??? Is this legit? And even if their claims are exaggerated, what is there to lose?