Is this the beginning of the end for Facebook?

Facebook’s daily active user number in the U.S. and Canada fell for the first time ever in Q4. 

The social network boasted 185 million daily users in those countries in the last quarter, dropping by a million to 184 million in the most recent quarter. 

Why has this number dropped? 

Is this good or bad? 

Is this the beginning of decline for the world's biggest social network?