Facebook is now showing a right sidebar module called “Friends’ Photo Albums” which displays photos uploaded by the friends a user interacts with most. However, unlike many of Facebook’s modules such as Unread Messages or Photo Memories, Friends’ Photo Albums appears on a user’s news feed, as well as other in-house apps such as Events, photos, and Groups.

Facebook appears to be using the module to get users to click away from their home page and get deeper into the site’s other features.

Some in-house app modules Facebook has tried in the last few months include Recent Checkins and Related Photos. The Friends’ Popular Places module was tested on the home page, and a Questions module now permanently resides in the center of the home pag right sidebar. Facebook also displays app specific modules such as Event Invitations while browsing Events, or Deals while browsing Places pages.

Facebook’s rapid development, testing, and deprecation of these modules suggests the site is searching for the most effective ways of getting users to navigate across different in-house apps, which likely reduces exhaustion and increases time-on-site.

Users will now see the module while browsing the news feed, Photos, Groups, Events, Friends, Notes, and Applications. It seems that page real estate is being shifted away from People You May Know, an early sidebar module which is helpful for new users, but which provides less utility to veteran users who’ve already found most of their friends.

Typically the module shows two sets of two photos, accompanied by the uploader’s and album’s names. However, when seen while browsing Applications, the module can show up to five sets.

Clicking through the photos does not bring up the lightbox view which is designed to keep a user’s place within Facebook while they view photos, and instead navigates users to the old photo browser. This indicates that the goal of the module may be to give users a compelling transition to Photos instead of them leaving the site when they’re done using an in-house app.

[Thanks to Eti Suruzon for the tip]