Amazon caught the media's attention a few days ago when it announced its new Kindle tablets on Sept. 6, but one thing seems to have slipped under the radar: Bing will be the default search engine across all new Kindle Fire models.

UnberGizmo was the first to notice, at Amazon's press conference in Santa Monica, that the default search engine used in the search box of the Web browser was not Google's search engine, but Microsoft's Bing. Both Microsoft and Amazon have since confirmed that all Kindle Fire tablets will ship with Bing as the preset default for the search box. The default engine in the original Kindle Fire released last year was Google, but Amazon said Bing will now replace it in the new line.

"All text you enter in Amazon Silk's address bar is sent to a default search engine," Amazon details in its terms and conditions regarding the Silk browser. "The initial default search engine is selected by Amazon Silk, and we may change the default search engine in the future without notice to you," explains the company. "If you would like, you may choose to use a different search provider as your default search engine."

In other words, Amazon can switch out the default search engine at any given time, but so can users. Having Bing featured in such a strong position on all Kindle Fire tablets is a big win for Microsoft, and the software giant is likely paying a significant amount of money to Amazon for this.

This kind of deal typically amounts to millions of dollars each year. When Google signed a deal with Mozilla back in December 2011, it agreed to pay roughly $300 million per year to Mozilla to have its search engine featured within the Firefox Web browser. Moreover, various rumors indicate that Google is paying Apple more than $1 billion per year in revenue sharing in order to have its search engine as the default on all iPhones and iPads.

Microsoft launched its Bing search engine back in June 2009, but has had a tough time grabbing market share from the all-mighty Google. According to data from Net Applications, over the last eight months Bing held a 4.4 market share on desktops and laptops, and a 1.1 percent market share on tablets and mobile devices. Meanwhile, Google is dominating the space with roughly 80 percent market share on desktops and over 90 percent on mobile devices.

As usual, comScore's data shows otherwise, and its measurement scale specific to the U.S. shows more positive stats for Microsoft. Based on comScore's data, Microsoft he;d a 15 percent market share for searches at work and home, while Google still dominated with 67 percent.

Having Bing as the default search engine on all Kindle Fire tablets may change these figures and have a positive impact on Bing's popularity. Users can change their default search engine at any given time, but not all users bother to do so.