As an additional tidbit here, the -p 8787:8787 is responsible for this. It says "map my local port 8787 to port 8787 on the container". For instance, if you used -p 8888:8787, then you would access the browser at http://localhost:8888 
Also, docker inspect container_name is a handy way to get lots of information about the container
The IP doesn't help a bunch in this case because often the docker network is a different one than your browser is using (of course, that is all configurable, but is complicated).
In any case, suffice it to say that -p someport:serviceport is your friend when you need to access a service running in docker locally! 