Two months after rolling out hashtags — key words in posts that are marked by “#” – Facebook is experimenting with new ways to make them useful. The social network has begun testing a “trending” topics section in the homepage news feed of its website. The section — similar to rival Twitter’s “trends box — showcases topics, including hashtags, that are currently popular on the site. A Facebook spokeswoman confirmed the test on Friday. “We are running a small test of a unit on News Feed,” she said. “Right now it only available to a small percentage of US users and it is still in the early stages of development.” She said Facebook will disclose more details if it decides to release the feature more broadly. The test, which began on Thursday, highlights the escalating brawl between Facebook and Twitter to be the dominant destination for live, real-time conversations online.