Google has long been the default engine on the Firefox search bar, generating the vast majority of Mozilla's total revenue (close to 90% in 2007), but things have become "complicated" between the two ever since the release of Chrome back in September. This has urged the company to develop other revenue streams, in an effort to become less dependent on Google, as it steps up the fight for browser market share amid increased competition.
It's not much of a surprise, then, to hear news that Firefox users in Russia are about to see a different set of search results after the Mozilla Foundation ditched Google there in favor of local specialist Yandex. The move, however, was not purely aimed at dealing a blow to Google (after all the two still have an advertising deal in place through 2011) but was rather the result of feedback indicating Russian users really wanted direct access to the Yandex search services.
The service is due to debut as the default search provider in Firefox 3.1 soon. Details of the change are mentioned in the Mozilla bug tracker, which specifically refers to "the new business arrangement between Mozilla and Yandex in Russia."