--- a/servo/components/style/gecko/wrapper.rs
+++ b/servo/components/style/gecko/wrapper.rs
@@ -402,16 +402,34 @@ impl<'lb> GeckoXBLBinding<'lb> {
 pub struct GeckoElement<'le>(pub &'le RawGeckoElement);
 
 impl<'le> fmt::Debug for GeckoElement<'le> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         try!(write!(f, "<{}", self.get_local_name()));
         if let Some(id) = self.get_id() {
             try!(write!(f, " id={}", id));
         }
+
+        let mut first = true;
+        let mut any = false;
+        self.each_class(|c| {
+            if first {
+                first = false;
+                any = true;
+                let _ = f.write_str(" class=\"");
+            } else {
+                let _ = f.write_str(" ");
+            }
+            let _ = write!(f, "{}", c);
+        });
+
+        if any {
+            f.write_str("\"")?;
+        }
+
         write!(f, "> ({:#x})", self.as_node().opaque().0)
     }
 }
 
 impl<'le> GeckoElement<'le> {
     /// Parse the style attribute of an element.
     pub fn parse_style_attribute(value: &str,
                                  url_data: &UrlExtraData,