Expanding on >>3875091 (pb)
re: Facebook share price history
5-year, 1-year and 5-day history graphs capped for context.
The big drops were latter half of March, more than made up by a big increase (at a higher rate than historical trends), then the big drop July 26. Since then FB has been on a downward trend.
I would say today's drop wasn't all that notable in that context, and fits in the overall downward trend – the only thing that makes it notable is that it hit a milestone ("lowest point since xx"). If anything the continued downward trend since August is more notable.