It slid in January of last year as well. Is it a seasonal effect? (can't find FB's older figures.. I'm not good in digging up this kind of information)
https://www.statista.com/statistics/267606/quarterly-revenue...
https://www.statista.com/statistics/422035/facebooks-quarter...
https://www.statista.com/statistics/273963/quarterly-revenue...
https://www.statista.com/statistics/272746/microsoft-corpora... (keep in mind that Microsoft's fiscal calendar is different, so it ends up being the same time of year)