When you think of Google and Mozilla you probably think of them as Web browser rivals. On the one side, you have Google with Chrome; on the other, Mozilla with Firefox. Or, looking ahead, you might see them as mobile operating system competitors with Google's Android vs. Mozilla's Firefox OS . But, have you looked at Mozilla's financials? You should.

If you do, you'll find that more than 90 percent of Mozilla's revenue comes from Google. Yow!

I wasn't sure my math was right so I checked with Mozilla. I was right.

A Mozilla spokesperson told me, "Mozilla's search agreement with Google accounted for approximately 90 percent of our 2012 royalty revenue, as disclosed in our annual financial statement."

True, Mozilla also made some money from its Bing, Yahoo, Yandex, Amazon and eBay partnerships. Mozilla won't say specifically how much it made from these partners. The Mozilla representative said, "The specific terms of our commercial agreements with search providers are subject to traditional confidentiality requirements, and we’re not at liberty to disclose them." Still, no matter how much it is, even pooled together, Google's revenue dwarfs it.

In addition, Mozilla stated that "A growing percentage of our revenue also comes from support from the public, including grants and individual donors like you." Actually, that's not quite right. In 2012, Mozilla's total revenue was $311-million(PDF Link), but only $855,000 came from unrestricted contributions. So, far less than 1 percent of Mozilla's revenue comes directly from grants and supporters.

Add it all up and Mozilla is doing quite well. In 2011 its revenue was $163 million. So, in 2012, Mozilla's revenue went up more than 90 percent. At the same time, while Mozilla's expenses have also grown, from $145 million in 2011 to $208 million in 2012, but its income has far outpaced its expenses.

There's only one little problem with all this. Mozilla has almost all its financial eggs in Google's basket.

True, it's almost billion-dollar Google search search advertising contract won't expire until 2014, but over the years Mozilla has grown to depend more and more on Google. In 2010, 84 percent of its revenue came from Google; in 2011, it was 85 percent, and in 2012 it came to just over 90 percent. That's not healthy.

Yes, Mozilla goes its own way. Unlike Opera, which has adopted Google's Blink for its Web browser engine , Mozilla isn't giving up on its Gecko engine. In addition, Mozilla is working hard on making Firefox OS a serious contender for the third spot in the mobile operating system race. Eventuallly, Firefox OS may even be an Android rival.

Still, if you care about Mozilla, you really have to worry about its future. As Mozilla grows ever more dependent on its Google cash-flow, you have to worry about just independent Mozilla can be in the long run.

Is Mozilla a branch of Google today? No. Could they become one? Well, let's see what Mozilla can do about finding other revenue streams between now and when its Google contract runs out and we'll see what we see.

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