From the survey:

When double checking on the browser support for String.prototype.includes, the visuals made it look like Fireforx did not support it, as there was no green. You had to click a red arrow element at the bottom to see that it was in fact supported from v 40 on; the dominant visual information was the non-standard contains method for versions 18-48

The ordering in the array is wrong: https://github.com/mdn/browser-compat-data/blob/master/javascript/builtins/String.json#L906 version_added: 40 needs to be the first element.