If you’re visiting any Yahoo property today, chances are you’ll see an “Upgrade to the new Firefox” link in the top-right corner of your browser window. The prompt also appears if you’re using Internet Explorer, Opera and even the new Yandex browser. However, the prompt is missing from Safari, which will surely prompt a new round of speculation about Apple’s rumored switch to Yahoo as its default search engine.

Given that Firefox now uses Yahoo as its default search engine, this move doesn’t come as a huge surprise. Yahoo clearly wants as many people as possible to use Firefox — and with it its search engine (which is powered by Microsoft Bing).

Firefox’s user share has dropped quite a bit over the last few years, so Mozilla has no objections to putting the Firefox logo in front of as many Yahoo users as possible. Changing the default search engine in Firefox is trivial (and Firefox recently made it even easier), but most users never bother to make the switch. The new Yahoo Search design for Firefox users also looks pretty much exactly like Google’s, so some users may not even notice the difference.

It’s still too early to know whether the Yahoo/Mozilla deal made any difference in terms of market share for either of the two organizations, but chances are we’ll see at least a small uptick in Yahoo’s numbers come January.

Props to our awesome copy editor Catherine Pickavet for spotting this change.