diff --git a/toolkit/components/printing/content/printPreviewToolbar.js b/toolkit/components/printing/content/printPreviewToolbar.js
index 46d31d10005e..06b2b8d10f94 100644
--- a/toolkit/components/printing/content/printPreviewToolbar.js
+++ b/toolkit/components/printing/content/printPreviewToolbar.js
@@ -65,11 +65,9 @@ customElements.define("printpreview-toolbar", class PrintPreviewToolbar extends
       <toolbarseparator class="toolbarseparator-primary"/>
       <button label="&close.label;" accesskey="&close.accesskey;" oncommand="PrintUtils.exitPrintPreview();" icon="close"/>
       <data id="print-preview-prompt-title" value="&customPrompt.title;"/>
-    `, `
-    <!DOCTYPE bindings [
-      <!ENTITY % printPreviewDTD SYSTEM "chrome://global/locale/printPreview.dtd" >
-      %printPreviewDTD;
-    ]>`));
+    `, [
+      "chrome://global/locale/printPreview.dtd",
+    ]));
 
     this.mPrintButton = document.getElementById("print-preview-print");
 
diff --git a/toolkit/content/customElements.js b/toolkit/content/customElements.js
index 44a9b46c674c..8773aa8601c9 100644
--- a/toolkit/content/customElements.js
+++ b/toolkit/content/customElements.js
@@ -24,8 +24,8 @@ class MozXULElement extends XULElement {
    * This process is required instead of calling the createElement method directly
    * because bindings get attached when:
    *
-   * 1) the node gets a layout frame constructed, or
-   * 2) the node gets its JavaScript reflector created, if it's in the document,
+   * 1. the node gets a layout frame constructed, or
+   * 2. the node gets its JavaScript reflector created, if it's in the document,
    *
    * whichever happens first. The createElement method would return a JavaScript
    * reflector, but the element wouldn't be in the document, so the node wouldn't
@@ -33,18 +33,24 @@ class MozXULElement extends XULElement {
    * document, it won't get XBL attached until either the frame is constructed or
    * the reflector is garbage collected and the element is touched again.
    *
-   * @param str
+   * @param {string} str
    *        String with the XML representation of XUL elements.
-   * @param preamble
-   *        String to be inserted above any markup. This can be used
-   *        to insert XML entity text, for instance.
+   * @param {string[]} [entities]
+   *        An array of DTD URLs containing entity definitions.
    *
-   * @return DocumentFragment containing the corresponding element tree, including
-   *         element nodes but excluding any text node.
+   * @return {DocumentFragment} `DocumentFragment` instance containing
+   *         the corresponding element tree, including element nodes
+   *         but excluding any text node.
    */
-  static parseXULToFragment(str, preamble = "") {
+  static parseXULToFragment(str, entities = []) {
     let doc = gXULDOMParser.parseFromString(`
-      ${preamble}
+      ${entities.length ? `<!DOCTYPE bindings [
+        ${entities.reduce((preamble, url, index) => {
+          return preamble + `<!ENTITY % _dtd-${index} SYSTEM "${url}">
+            %_dtd-${index};
+            `;
+        }, "")}
+      ]>` : ""}
       <box xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul">
         ${str}
       </box>
diff --git a/toolkit/content/widgets/textbox.js b/toolkit/content/widgets/textbox.js
index 5355000dc624..c07fabb868e0 100644
--- a/toolkit/content/widgets/textbox.js
+++ b/toolkit/content/widgets/textbox.js
@@ -8,10 +8,9 @@
 
 const cachedFragments = {
   get entities() {
-    return `<!DOCTYPE bindings [
-      <!ENTITY % textcontextDTD SYSTEM "chrome://global/locale/textcontext.dtd">
-      %textcontextDTD;
-    ]>`;
+    return [
+      "chrome://global/locale/textcontext.dtd",
+    ];
   },
   get editMenuItems() {
     return `