For over a year, the all-powerful Facebook has been the top social media site driving Web traffic in the U.S. But this past month, Facebook fell to second place , GigaOM reports.
According to global Web analytics service StatCounter, Web discovery engine StumbleUpon is now the biggest traffic driver among social media websites in the U.S. Data shows  that StumbleUpon dethroned Facebook in mid-June, with StumbleUpon now driving around 49 percent of traffic and Facebook falling to 37 percent.
StumbleUpon, which was founded in 2001, was sold to eBay in 2007 for $75 million before its co-founders bought it back along with a group of investors in 2009. Since then, the site has been working “quietly and diligently” at a comeback, says GigaOM.
Back in February, StumbleUpon briefly surpassed Facebook in StatCounter hits for two weeks, but Facebook was quickly back on top. This time, StumbleUpon is regaining traction at the same time that Facebook users are fleeing the site and Twitter is apparently having trouble getting its own users to stick around—which could mean that StumbleUpon might hold onto the top spot for a little longer.