In a seemingly minor tweak to Facebook’s search results, the company is testing the addition of some key new details in its drop-down menu, or so some users are starting to spot. When you start typing letters into the search box in the top navigation bar, you’ll see — as before — a list of friends, applications, Pages and groups you’ve added that contain the letters.

[Update: Facebook is now starting to push the change out to all users. More, from the Facebook blog:

But now, for friends, you won’t just see their names and networks they’re in, you’ll also see the number of mutual friends you have with them, and the names of two of these people. This should help users more quickly identify who they might be searching for.

For applications, you’ll see the number of monthly active users each app has. Facebook has also been emphasizing games separately from other apps in its new Games Dashboard, and this classification is reflected in the new drop-down menu. Any app that self-identifies as a game in Facebook’s in classification schema will be listed as “Game.” Otherwise, it will be listed as “Application.”

Also, all results in the drop-down menu now have larger icons than before.

We say this is a “seemingly minor” change because Facebook has been busy making its search features more valuable lately. In the home page redesign it launched in early February, it moved the search box from the left-hand side of the site to the middle, and made it bigger. The company is also working with strategic investor Microsoft to deliver more relevant results based on social data.

And, due to redesigns or overall growth, Facebook is continuing to increase its share of the US search market. Web measurement firm comScore reported that Facebook had grown its on-site search volume by 13% for January and another 10% in February. Each of these little changes may seem small, but they help make search a generally more valuable component of the service — and for applications, these new details might lead users to engage with applications more often.