Check your Firefox settings. Make sure that "release" is the Update Channel. The 1st and 3rd options below work to find the setting. The 2nd option is too indirect. The paragraph about the installer applies for the latest version, not just 56.0.1. The write up is from a a few releases ago, the rest is still current. Oh, this is screen snip so the links aren't links, just a picture.
This is what you get after using the 1st or 2nd method;