Mozilla, the organisation behind the Firefox web browser, counts Google as its biggest source of revenue.

In fact, last year, the search giant was responsible for the vast majority (84%) of Mozilla’s $123m in revenue.

The relationship between the two high-profile technology outfits is simple; Mozilla makes Google the default search engine in Firefox, and in return, Google shares revenue generated by Firefox-driven searches.

Thanks to a new three year agreement announced yesterday, this relationship will remain in place under financial terms that are undisclosed.

But it’s getting more complicated. The reason? Google is now one of Mozilla’s biggest competitors thanks to the rise of Google’s Chrome web browser.

Chrome’s rise has impacted Firefox the most. While Microsoft’s Internet Explorer is managing to maintain its market share, most of Chrome’s growth has come at the expense of Firefox – which according to StatCounter, was surpassed by Chrome globally in market share in November for the first time ever.

It’s unclear what Mozilla can do to put a dent in Chrome’s momentum. The organisation continues to release improved versions of its browser, and it’s sticking to a rapid release cycle that, in theory, makes it easier to deliver its improvements to market. But none of this seems to be thwarting Chrome, which must make Mozilla’s relationship with Google somewhat uncomfortable. After all, when the competitor eating your lunch is effectively keeping food on the table, what can you do?

Mozilla’s decision to renew its search agreement with Google was, of course, pragmatic. Although it has search agreements with other major search engines, there’s little doubt that Google can deliver more revenue than a Yahoo or Bing. But if Mozilla is going to have a meaningful position in the market in three years, it had better figure out a way to put some of that revenue to use in stopping Chrome. And quick.