In tech, little things can have big consequences — in this case, a tiny search bar. Last night, Firefox made a surprising announcement: after 10 years with Google as its default search engine, it would be handing the tiny search bar over to Yahoo. On the face of it, it's a strange move. If you're looking for almost anything on the internet, Google is a much better way to find it than Yahoo is. But that small search bar isn't just a feature, it's a business. And it’s a business that reveals how Mozilla and Google could increasingly be at odds with each other.

For the last 10 years, Google has had that business almost entirely to itself. Every time you make a search through that bar, Google makes a little bit of money from ads and passes a piece of that money on to the browser through AdSense's revenue sharing deal. That adds up to hundreds of millions of dollars for companies like Mozilla, but the money can produce some strange incentives. Google's making a browser too, and it may not want to support Chrome's competitors forever. Suddenly, the short-term money starts to look like a long-term liability.

For Mozilla, that's a frightening prospect — and one that played a big part in yesterday's announcement. When Mozilla CEO Chris Beard explained the decision, he did it under the headline "Promoting choice and innovation on the web." Reading between the lines, that means choice in areas where Google is increasingly becoming the default option: browsers and search. For Google, those projects are just part of a larger picture, necessary steps in a seamless ecosystem that's being built across Chrome, Android, and services like Gmail. But that unified platform would leave no place for Mozilla and Yahoo.

Smaller projects are already feeling that threat. This January, Google rolled out a technical update to AdSense that killed the ability to mask a user's IP address. For Google, it was a way to crack down on fraud — a minor update — but it shut one privacy project out of Adsense entirely. Epic makes a browser that hides your IP address from the sites you visit. It's not a hugely popular service, but for the program's roughly 10,000 users, it's a useful one. Thanks to the Google search bar, Epic could also make money from its browser, provided it verified user IPs with a third party called Blucora to make sure they were all real people.

But when Google made its update, the system broke down, and now Epic is left scrambling for a new way to make money. As CEO Alok Bhardwaj told The Verge, "I think their hope is that us and any other browser disappears." But without some sort of relationship with Mountain View, it's not clear how Epic and other projects like it can survive. You can still make an IP-masking browser, but you can’t get Google money for the search bar. And in a market full of free -- or rather, AdSense-funded — browsers, that puts privacy-minded users and developers at a serious disadvantage.

For Mozilla, Epic's story reads as a warning. We aren't about to see an IP-masking version of Firefox, but there are plenty of other issues like Do Not Track where Mozilla's Free Software ethos might conflict with Google's need for continually smarter and more targeted ads. There's straightforward competitiveness, too: every Firefox user is someone who isn't using Chrome. None of that has bubbled up into outright conflict yet, but it could — and as long as Mozilla is getting a huge chunk of its money from AdSense, it would be at a disadvantage in any fight that arose.

If you're looking for other options, Yahoo is a natural choice. There have been rumors that Marissa Mayer wants to restart Yahoo's search business, particularly as the company's partnership with Bing seems less and less binding. When the news broke, Mayer teased future product integrations in the works between the companies, so maybe we'll see more in the months to come, but the most attractive thing about Yahoo may have simply been that it doesn’t run a browser. While Google swallows up everything in its vicinity — laptops, DNS servers, fiber networks — Yahoo's ambitions are a lot less dangerous for a humble browser like Firefox.

The big question is, will it be enough? Can Firefox and Yahoo successfully fend off Google's giant ambitions? Will this drive more users to Firefox or just slough them off to Chrome? When Yahoo's new search rolls out in December, will it convince anyone to switch sides? Or will enough users switch their default search back to Google and possibly cut down the money Yahoo is sending Mozilla’s way? It will be a tough fight, but in the end, Mozilla doesn’t have to beat Google — it just has to keep the fight going.