For those of you who don’t think twice about your browser’s default search engine, meet the people who do.

For most Internet users, you don’t give a second thought to your browser’s default search engine. Internet Explorer defaults to Bing, Chrome defaults to Google, and Firefox defaults to Google as well. For most of us, “to Google” has become synonymous with “to search.” Unbeknownst to most of us Internet surfers, Google and Firefox’s relationship hasn’t always been so chummy.

In 2009, Eric Schmidt (CEO of Google) responded to an interview question by saying “If you have something that you don’t want anyone to know, maybe you shouldn’t be doing it in the first place.” Many Internet users cried foul, that someone in charge of so much of the information in the world would dismiss privacy concerns so quickly. Particularly, the product head of Mozilla Asa Dotzler was unhappy with the flippancy with which Schmidt talked about privacy.

Fast forward to November 2011. Google and Mozilla have had a revenue-sharing agreement for years which expired in the end of November. Reports indicated that 84% of Mozilla’s revenue comes from the money Google pays them to have their search be the default search in Firefox. And it wasn’t just a one-sided deal. Every click that Google got to their search results page kicked back some money to Google, due to ad revenue. And who would Mozilla turn to if Google were to leave? Bing.

It’s amazing to think that just five short years ago, Firefox was the original alternative browser to Internet Explorer, and in late November there they were, contemplating making a deal with the very company they were trying to take users from in the first place. For that very reason, analysts laughed at the idea that Google would walk away from their Mozilla deal and let almost 40% of Internet users that use Firefox see Bing everyday. Not only would they lose a large chunk of revenue, but it would be handing Microsoft money on a silver platter.

In the end of the negotiations, all was as it should be. Google and Mozilla signed a three-year deal proclaiming Google the default search engine on all downloaded Firefox browsers. The deal reportedly nets Mozilla $300 million a year. Of course, users can still change their default search settings, and Mozilla even released a Bing-specific version of Firefox to interested users in October.

The question remains: why would Google still be interested in this deal when they have their own browser that competes with Firefox? Wouldn’t they want to cut off supplying money to their competitor? The answer is simple: they make enough themselves to make it worthwhile. Google gets a pretty penny from what they invest into being Firefox’s default search engine. Every person that sees a Google search results page sees ads from Google, which generates revenue. Dotzler explained that Google uses about 24% of its ad profit to drive more ad sales. And Firefox isn’t the only default browser engine Google is paying for. They have similar contracts with Apple’s Safari browser and the Opera browser.

Google developer Peter Kasting told Webmonkey that Google’s main goal for Chrome isn’t to be the most popular browser (although, I’m sure they wouldn’t be complaining if they did reach that milestone). Kasting said that Google’s primary goal is to advance the web, much like Firefox’s goal when they first arrived as another option for web browsing. If they are never a very popular browser but drive web browser’s to do more, better, then Kasting says, mission accomplished.

No matter which browser you use to check Facebook or read your favorite blogs, Google has become a household name. The sad truth for search engine competitors is that even when people use Bing or Yahoo Search, they usually still say they’re “googling.”