Not sure whether this is useful because 'data visualization' can mean a lot of things, but we first built customized charts using D3 (nothing as fancy as Jacob's code example) and then we stumbled on Keen.io.
(I have no affiliation by the way, but we found it super useful and it let us spit out dozens of analytics charts).
There was a good tutorial on Keen/Firebase integration which inspired us:
The nice thing about Keen is they integrate with D3, C3, and Google charts and they DO make it super simple to spin out a bunch of visualizations.
Hopefully this is somewhat useful, I guess it depends what you want to 'see' with visualizations but for our purposes it was a good/fast way to create some useful analytics.