After Mozilla inked the deal with Yahoo, the eyes turned to Apple and its Safari browser. Currently, the default search engine is Google on both iOS and OSX, although Bing is the primary engine used for other functions, like Siri and Spotlight. Until early 2015, they are tied into a contract with Google for those two browsers, but who will get the new contract?
Apparently Yahoo and Microsoft have both approached the company for the position, and Apple is not ruling any of the three out. Probably the most interesting part is how Yahoo is genuinely taking the search business seriously. The deal with Mozilla is fairly long-term, and with Yahoo approaching Apple as well, it probably was not just charity on Mozilla's part because no-one else wanted to be Firefox's default. Yahoo would probably need some significant monetary backing for an Apple deal, which suggests the same for their deal with Mozilla.
If both Mozilla and Apple leave Google, it will take a significant chunk out of the search engine. Power users, like those who read this site, will likely be unaffected if they care, because of how low the barrier is to change the default search engine. On the other hand, even the most experienced user will often accept default settings until there is a reason to change. The winning party will need to have a good enough product to overcome that initial shock.
But the money will at least give them a chance when the decision comes into effect. That is, unless the barrier to changing default search engines is less than the barrier to changing default web browsers.
Google will always be default on Google Chrome.