Run this script in Scratchpad in Latest Nightly to get a key-value pair of all the prefix-free properties vs their possible standard values.

CSSPropertyValueScratchpad.js

/* -sp-context: browser */
let domUtils = Cc["@mozilla.org/inspector/dom-utils;1"].getService(Ci.inIDOMUtils)
let properties = {};
domUtils.getCSSPropertyNames(domUtils.INCLUDE_ALIASES)
        .sort()
        .filter(x=>!x.startsWith("-moz"))
        .forEach(x=> {
  properties[x] = domUtils.getCSSValuesForProperty(x)
                          .sort()
                          .filter(x=>!x.startsWith("-moz"));
});
JSON.stringify(e)