Fixing selection issues in Firefox

lib/web_ui/lib/src/engine/text_editing.dart

@@ -341,6 +341,7 @@ class TextEditingElement {
       _subscriptions.add(domElement.onKeyUp.listen((event) {
         _handleChange(event);
       }));
+      _subscriptions.add(domElement.onSelect.listen(_handleChange));
     } else {
       _subscriptions.add(html.document.onSelectionChange.listen(_handleChange));
     }
@@ -379,7 +380,7 @@ class TextEditingElement {
         throw UnsupportedError(
             'Unsupported input type: ${inputConfig.inputType}');
     }
-    html.document.body.append(domElement);
+    domRenderer.glassPaneElement.append(domElement);
   }
 
   void _removeDomElement() {

lib/web_ui/test/text_editing_test.dart

@@ -75,6 +75,9 @@ void main() {
       expect(document.activeElement, input);
       expect(editingElement.domElement, input);
 
+      // Input is appended to the glass pane.
+      expect('${editingElement.domElement.parent.tagName}', 'FLT-GLASS-PANE');
+
       editingElement.disable();
       expect(
         document.getElementsByTagName('input'),