Many Facebook users are seeing the site’s top navigation bar locked to the top of the browser window no matter where they scroll. This floating navigation bar gives users access to their notifications, friend requests, messages, and links to the home page, profile, and account settings at all times. Previously, if users scrolled down the news feed, a profile, or other page on the site the top navigation bar would scroll with it and become hidden from view.

[Update 9/16/2011 8:30pm PST: Some users that saw the floating navigation bar yesterday are now seeing it moving with the rest of the site chrome when they scroll. Yesterday's test may have been designed to gauge reactions from users, with Facebook seeing if users clicked the top navigation buttons more frequently with the floating design.

The feature could be officially launched at f8 next week, though there's also the chance that this temporary test is the last we'll see of a floating Facebook navigation bar. The expansive but temporary roll out is certainly atypical for Facebook, though.]

By giving users access to navigation functions even when they’re scrolled down a page, Facebook may be able to reduce the likelihood that they’ll leave the site when they finish viewing something. Instead, they’ll be tempted to visit another part of the site, especially if they have pending notifications, requests, or messages.

Users may recognize the floating navigation bar as it’s used on both Twitter and Google+. Some might say this is one more way Facebook has followed the lead of its competitors when its comes to design.

Users may also notice that while playing certain social games such as CityVille, their right sidebar that contains the games ticker and ads stays fixed when they scroll. This is not the case on all games and apps or at all window widths, though. We believe the fixed sidebar for games depends on how third-party developers utilize the fluid canvas option released last month, and is not related to Facebook’s cross-site implementation of the floating navigation bar.

The rollout of persistently visible navigation options, along with several recent product releases and site changes, could be groundwork for a more significant redesign to be launched at f8 next week. Rather than shock users by changing many things about the site at once, Facebook may be opting to push changes one at a time.

Facebook tested a design of the news feed a few months ago that removed the Most Recent feed and locked both the top navigation bar as well as the left navigation bar of bookmarks. If our theory holds true, Facebook might be trying to get users accustomed to the fixed navigation bar before it alters the news feed at f8.

It’s safe to assume that removing the second tab of the news feed would significantly alter user behavior and cause some backlash. Minimizing additional confusion by keeping other design elements stable, even if just for a week, could increase the chances of a successful reception.

We’re seeing the locked navigation bar across our accounts, so it may have been rolled out to a majority or all of the user base. If you’re not seeing it yet, or have feedback on the new design, let us know in the comments.

[Thanks to Dan Birdwhistell for the tip]