Once upon a time, no one questioned which browser ruled the land—it was Microsoft’s Internet Explorer (IE). Not so anymore, according to a new report from Adobe Digital Index (ADI). Google’s browsers, which already had the lead outside of the U.S., has overtaken IE in the United States for the very first time.

According to ADI’s latest analysis of Web browsers, Google now commands a 31.8% market share—desktop and mobile, combined—which is up 6% year-over-year (YoY). IE sits at 30.9%, down by 6% YoY, while Apple’s Safari, thanks to its vast mobile presence, is the third most popular browser, with a 25% share.

“Control of the browser gives Google an even greater role in consumers’ lives,” said Tamara Gaffney, principal analyst at ADI. “Not only do the Chrome and Android browsers both default to Google search, but with their Gmail and Google+ extensions, consumers are spending more and more time signed into Google’s ecosystem.”

Mozilla’s Firefox browser—which consistently held a minor, yet steady, position—declined from nearly 20% market share two years ago to only 8.7% in April. According to ADI, this decline is likely due to its lack of mobile presence.

ADI’s report is based on aggregate and anonymous data across retail, media, entertainment, financial service, and travel Web sites. Adobe Analytics was used to detect the browsers for 17 billion visits to 10,000 U.S. consumer-facing Web sites in April 2014, and more than 1 trillion visits since 2008. (Note: Adobe is CMO.com’s parent company.) Market share figures represent the share of visits from each browser for the average U.S. Web site.

ADI technology analyst Tyler White speculated that two underlying market forces are at play. “First, device defaults matter,” White said. “Internet Explorer leverages its Windows OS dominance to gain share as the default Web browser for the majority of people online. Today mobile OS is more important, giving Google and Apple a leg up with default status on Android and iOS.”

The second reason why Google is growing, White said, is that “users prefer a consistent experience across devices.” Chrome, which is rumored to become the default browser on all Android devices in the near future, offers a consistent interface with sharable bookmarks in a fully functional browser capable on desktop and mobile.

Google has seen even more success outside of the U.S., where it took over the market share lead last year. In 2011 Google began to climb in Brazil, Mexico, Spain, Russia, and Italy, which, according to White, corresponds with the use of Android phones outside the U.S.

“Marketers need to be aware of browser usage as they build digital properties,” according to White. “Understanding the types of devices people are using is crucial to customer experience.”

ADI’s analysis confirms that Apple continues to dominate mobile browsing: Safari Mobile is the most used mobile browser, taking a 59.1% share of the market.

“Apple,” White added, “is leveraging its mobile share, putting Safari in the spotlight at this week’s Apple Developer Conference.”

Apple’s emphasis on Safari underscores its realization that the browser wars are a major key to achieving default status control. It has likely noticed that Windows users are replacing IE with Chrome on the desktop and want to protect its share on iOS devices. However, Apple’s browser success currently remains limited to the mobile space. Safari Desktop has the smallest share of the four major desktop browsers, with 10.3% market share. IE Desktop is currently leading the pack, with a 43.3% share, while Chrome Desktop has 30.6% and Firefox Desktop has 12.5%.

“In the past, there was just one browser—Internet Explorer—and the others were insignificant by comparison—they just really didn’t matter,” Gaffney said. “Today, the market is fragmented. There are four big players, and there is a certain portion of the digital audience using each of them, depending on which device is in use at any given time. Marketers can no longer develop for a single browser—especially in the mobile space.”