Thanks to a partnership between Mozilla and Yahoo, Google has seen the largest drop in its share of the search market since 2009, Bloomberg reports — and amid rising tensions with Apple, further decline may be imminent.

Mozilla's Firefox web browser has historically come bundled with Google as its default search engine, but a five-year deal signed with Yahoo in November has seen Firefox automatically opting for the rival search engine instead. The result? Google's US market share has slipped to 75.2% from 79.3% — with Yahoo's up to 10.4% from 7.4%.

Bloomberg reports that Google is at its smallest share of the US web search market "since at least 2008" and, more significantly, that Yahoo is at its highest share since 2009.

Here's a graph showing search market share over the past year: StatCounter

Firefox is used by just 12% of Americans, and as illustrated above, Google remains the undisputed search-market leader. (Thirty-seven percent of Americans use Google's Chrome browser, and another 34% use Microsoft's Internet Explorer.) Nonetheless, the news will be seen as a win for Yahoo CEO Marissa Mayer, who has been struggling to turn the ailing internet giant around. And as The Wall Street Journal points out, this may just be the start for Google.

There are reports that Apple is considering dropping Google as its default search engine on the iPhone's Safari web browser. It's not clear what Apple might replace the search giant with, but whether Yahoo, Bing, or an in-house search, it would be a big loss for Google. The Journal reports that in December, more than half of all US mobile traffic came from Safari.

There's a precedent for this: Back in 2012, Apple replaced Google Maps with its in-house Apple Maps app. The software was terribly received and plagued with bugs — but Apple seems to have learned from its mistakes. The map data has been gradually improving, and Apple CEO Tim Cook eventually released an apology over the new app.

Cook was so angry over the Google Maps controversy that he reportedly fired a top Apple executive. If Apple is planning on ditching Google again, it's going to ensure the alternative it comes up with is up to the task.

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