diff --git a/b2g/chrome/content/forms.js b/b2g/chrome/content/forms.js
index b48f24a214e6..56292d98669d 100644
--- a/b2g/chrome/content/forms.js
+++ b/b2g/chrome/content/forms.js
@@ -235,7 +235,13 @@ let FormAssistant = {
 
     this._documentEncoder = null;
     if (this._editor) {
-      this._editor.removeEditorObserver(this);
+      // When the nsIFrame of the input element is reconstructed by
+      // CSS restyling, the editor observers are removed. Catch
+      // [nsIEditor.removeEditorObserver] failure exception if that
+      // happens.
+      try {
+        this._editor.removeEditorObserver(this);
+      } catch (e) {}
       this._editor = null;
     }