Don't initialize L10n.#elements eagerly since it's unused in MOZCEN…

…TRAL builds

It's not necessary to manually start translation in the Firefox PDF Viewer, and doing so would even cause problems there (see issue 17142).

web/l10n.js

@@ -23,7 +23,7 @@
 class L10n {
   #dir;
 
-  #elements = new Set();
+  #elements;
 
   #lang;
 
@@ -71,7 +71,7 @@ class L10n {
 
   /** @inheritdoc */
   async translate(element) {
-    this.#elements.add(element);
+    (this.#elements ||= new Set()).add(element);
     try {
       this.#l10n.connectRoot(element);
       await this.#l10n.translateRoots();
@@ -91,10 +91,13 @@ class L10n {
 
   /** @inheritdoc */
   async destroy() {
-    for (const element of this.#elements) {
-      this.#l10n.disconnectRoot(element);
+    if (this.#elements) {
+      for (const element of this.#elements) {
+        this.#l10n.disconnectRoot(element);
+      }
+      this.#elements.clear();
+      this.#elements = null;
     }
-    this.#elements.clear();
     this.#l10n.pauseObserving();
   }