Passing variables from .user.js to js script, works fine in Tampermonkey but not in Greasemonkey

Question

I've been looking around trying to find why chrome will properly hand off variables from the .user.js but Firefox will not. Below is my code that I've been working on and I can't seem to figure out the difference between the two browsers.

User JS

// ==UserScript==
// @name        Highlighter Public Test
// @namespace   https://ashencloud.net
// @grant       none
// @include     https://*.google.com*
// ==/UserScript==

//**********************USER SETTINGS***************************//
searchTerm = "pie";

//**********************START DO NOT EDIT***********************//
var script = document.createElement("script");
script.src = "https://ashencloud.net/grm/highlighter_public/search.js";
document.getElementsByTagName("head")[0].appendChild(script);
//**********************END DO NOT EDIT*************************//

Search JS

// Create global variables for later
var timesRan = 1;
// Create function for general highlighting
// highlightWordGeneral will highlight the word even if it is part of the word or node
function highlightWordGeneral(word) {
    var xpath = "//text()[contains(., '" + word + "')]";
    var texts = document.evaluate(xpath, document.body, null, XPathResult.UNORDERED_NODE_SNAPSHOT_TYPE, null);
    for (n = 0; n < texts.snapshotLength; n++) {
        var textNode = texts.snapshotItem(n);
        var p = textNode.parentNode;
        var a = [];
        var frag = document.createDocumentFragment();
        textNode.nodeValue.split(word).forEach(function(text, i) {
            var node;
            if (i) {
                node = document.createElement('span');
                node.style.backgroundColor = "red";
                node.style.color = "white";
                node.appendChild(document.createTextNode(word));
                frag.appendChild(node);
            }
            if (text.length) {
                frag.appendChild(document.createTextNode(text));
            }
            return a;
        });
        p.replaceChild(frag, textNode);
    }
}
// Creates a function for searching all words at once later
function searchThings() {
  highlightWordGeneral(searchTerm);
}
//Creates a loop function that will run searchThings every 2000ms, stop after 30 times, and log it
function countRun () {                  //  create a loop function
   setTimeout(function () {             //  call a 3s setTimeout when the loop is called
      searchThings();                   //  run searchThings to find and highlight words
      timesRan++;                       //  increment the counter
      console.log("Searching...")       //  Log in the console to show evidence
      if (timesRan < 30) {              //  if the counter < 30, call the loop function
         countRun();                    //  ..  again which will trigger another
      }
   }, 2000)                             //  ..  setTimeout()
}
// Run function created above for countRun
countRun();

In Chrome, it's handing the variable from the .user.js to search.js fine. But in Firefox I'm getting "ReferenceError: searchTerm is not defined".

Any ideas as to what's different between Chrome and Firefox that would cause this kind of issue?