Yahoo syndicates their search index from Bing (Microsoft) and adds a little UI differentiation on top. I hate to say it, but Verizon/AOL could easily run Yahoo's heavily partner-dependent search business into the ground. I already hear peer feedback about them becoming more bureaucratic and less practical, and starting to alienate other partners. By the time Mozilla needs some leverage against Google I'm sure they will find a willing counterparty in Microsoft. It's unlikely they will ever have to deal with Yahoo directly again.