Userscript works in Tampermonkey on Chrome and Firefox, but doesn't work in Greasemonkey on Firefox - greasemonkey

Question

This script works just fine in Tampermonkey on both Chrome and Firefox, but doesn't work in Greasemonkey on Firefox. When I say it doesn't work I mean the button does not show up on the page. I'm using Chrome 61.0.3163.79 and Firefox 52.3.0.
The firefox console shows this warning but I'm not sure if it's relevant:
unreachable code after return statement[Learn More] jquery-1.3.2.min.js
Here's the code. Using greasemonkey on Firefox, I see "create button" in the console, but not "button has been created", which makes me think something is going wrong with the button creation. Any help greatly appreciated!
// ==UserScript==
// #name MyScript
// #namespace MyNS
// #description Adds a button to insert text into 2 text boxes
// #version 0.1
// #include *Removed for confidentiality*
// #compatible Greasemonkey
// ==/UserScript==
var descriptionText = "myDescription";
var testingText = "myTesting";
// Check if jQuery's loaded
function GM_wait() {
if (typeof unsafeWindow.jQuery == 'undefined') { window.setTimeout(GM_wait,100); }
else { $ = unsafeWindow.jQuery; init(); }
}
// All your GM code must be inside this function
function init() {
var description = $('#description');
var testingDone = $('#testing_done');
function insertText(template, editor) {
if (template) {
if (!editor._editing) {
editor.startEdit();
}
editor._field.queue(function() {
var oldVal = editor._field.val();
editor._field.val(template + (oldVal ? "\n" : "") + oldVal);
editor._field.keyup();
editor._field.dequeue();
});
}
}
function createButton(editor) {
console.log("create button:");
editor._insertTextButton = $('<input/>')
.attr('type', 'button')
.attr('value', 'Insert CR Template')
.css('margin-left', '1em')
.click(function() {
insertText(testingText, testingDoneEditor);
insertText(descriptionText, descriptionEditor);
});
console.log("button has been created");
editor._insertTextButton.insertAfter(editor._editIcon);
}
descriptionEditor = description.data('inlineEditor');
testingDoneEditor = testingDone.data('inlineEditor');
createButton(descriptionEditor);
}
GM_wait();