It looks like Facebook is again testing a new bit of functionality in its Android app with a subset of users. After the most recent update, people are suddenly seeing a built-in browser that loads timeline links rather than booting you out to a full browser. Whether this is a good thing or a bad thing depends heavily on how you feel about the Facebook app in general.
The browser appears to just be a WebView like many other apps use. Plenty of Twitter apps do the same thing when you open a link, for example. In this case, you get a drop down menu with forward/back buttons, copy link, open with, and save. So it's an extra step to get the link into a real browser, but Facebook gets to keep you in the app longer. That's really all it wants. If you wander off to the browser every time you open a link, you might get distracted and look at fewer ads on Facebook. That'd be a shame.
No one at AP is seeing this behavior as of yet, but it's widespread enough that we've gotten a few tips. It might roll out to everyone, or Facebook could pull it back and stick with the current system. We shall have to wait and see what the will of Zuckerberg dictates.