Facebook was down 0.3 percent after reporting fourth-quarter profits more than doubled to $3.7 billion due to strong growth in advertising revenues.
But the good results were offset by a Texas jury ruling that ordered Facebook and creators of its Oculus Rift to pay $500 million to gaming software firm ZeniMax in a lawsuit that claimed the virtual reality technology was stolen.
Among other large companies reporting earnings, ConocoPhillips lost 1.4 percent and Merck gained 2.6 percent.
About 20 minutes into trading, the Dow Jones Industrial Average had slipped to 19,869.10, down 0.1 percent.
The broad-based S&P 500 lost 0.2 percent at 2,276.23, while the tech-rich Nasdaq Composite Index fell 0.1 percent to 5,634.99.
Analysts expect the January jobs report to show the US added 170,000 jobs, with the unemployment steady at 4.7 percent.
Ralph Lauren Corp. slumped 11.2 percent as it announced chief executive Stefan Larsson will step down after barely a year due to creative disagreements with company founder Lauren.
Macy's gained 1.0 percent following a report in the New York Post saying the retailer was considering putting itself up for sale.