EDIT: Does anyone know why there's that spike for most of the benchmarks starting February 8th/10th? Seems like it affected both Chrome/Chromium and Firefox, although in some cases FF seems to have been hit the most. A Kernel update maybe? Some syscall changed?
Could be a readjustment in the metrics. They fix test and measurement errors from time to time and it often looks like a spike. They attach notes to the data points sometimes. Maybe clicking one of them during that time will shed some light.