--- a/layout/style/ServoBindingList.h
+++ b/layout/style/ServoBindingList.h
@@ -54,16 +54,18 @@ SERVO_BINDING_FUNC(Servo_StyleSet_Insert
 // CSSRuleList
 SERVO_BINDING_FUNC(Servo_CssRules_ListTypes, void,
                    ServoCssRulesBorrowed rules,
                    nsTArrayBorrowed_uintptr_t result)
 SERVO_BINDING_FUNC(Servo_CssRules_GetStyleRuleAt, RawServoStyleRuleStrong,
                    ServoCssRulesBorrowed rules, uint32_t index)
 
 // CSS Rules
+SERVO_BINDING_FUNC(Servo_StyleRule_Debug, void,
+                   RawServoStyleRuleBorrowed rule, nsACString* result)
 SERVO_BINDING_FUNC(Servo_StyleRule_GetStyle, RawServoDeclarationBlockStrong,
                    RawServoStyleRuleBorrowed rule)
 SERVO_BINDING_FUNC(Servo_StyleRule_SetStyle, void,
                    RawServoStyleRuleBorrowed rule,
                    RawServoDeclarationBlockBorrowed declarations)
 SERVO_BINDING_FUNC(Servo_StyleRule_GetCssText, void,
                    RawServoStyleRuleBorrowed rule, nsAString* result)
 SERVO_BINDING_FUNC(Servo_StyleRule_GetSelectorText, void,

--- a/layout/style/ServoStyleRule.cpp
+++ b/layout/style/ServoStyleRule.cpp
@@ -155,17 +155,22 @@ ServoStyleRule::SizeOfIncludingThis(Mall
   // TODO Implement this!
   return aMallocSizeOf(this);
 }
 
 #ifdef DEBUG
 void
 ServoStyleRule::List(FILE* out, int32_t aIndent) const
 {
-  // TODO Implement this!
+  nsAutoCString str;
+  for (int32_t i = 0; i < aIndent; i++) {
+    str.AppendLiteral("  ");
+  }
+  Servo_StyleRule_Debug(mRawRule, &str);
+  fprintf_stderr(out, "%s\n", str.get());
 }
 #endif
 
 /* CSSRule implementation */
 
 NS_IMETHODIMP
 ServoStyleRule::GetType(uint16_t* aType)
 {

--- a/servo/components/style/gecko_bindings/bindings.rs
+++ b/servo/components/style/gecko_bindings/bindings.rs
@@ -990,16 +990,20 @@ extern "C" {
                                                  reference:
                                                      RawServoStyleSheetBorrowed);
 }
 extern "C" {
     pub fn Servo_CssRules_ListRuleTypes(rules: ServoCssRulesBorrowed,
                                         result: nsTArrayBorrowed_uintptr_t);
 }
 extern "C" {
+    pub fn Servo_StyleRule_Debug(rule: RawServoStyleRuleBorrowed,
+                                 result: *mut nsACString_internal);
+}
+extern "C" {
     pub fn Servo_StyleRule_GetStyle(rule: RawServoStyleRuleBorrowed)
      -> RawServoDeclarationBlockStrong;
 }
 extern "C" {
     pub fn Servo_StyleRule_SetStyle(rule: RawServoStyleRuleBorrowed,
                                     declarations:
                                         RawServoDeclarationBlockBorrowed);
 }

--- a/servo/ports/geckolib/glue.rs
+++ b/servo/ports/geckolib/glue.rs
@@ -315,16 +315,23 @@ pub extern "C" fn Servo_StyleRule_AddRef
 }
 
 #[no_mangle]
 pub extern "C" fn Servo_StyleRule_Release(rule: RawServoStyleRuleBorrowed) -> () {
     unsafe { RwLock::<StyleRule>::release(rule) };
 }
 
 #[no_mangle]
+pub extern "C" fn Servo_StyleRule_Debug(rule: RawServoStyleRuleBorrowed, result: *mut nsACString) -> () {
+    let rule = RwLock::<StyleRule>::as_arc(&rule);
+    let result = unsafe { result.as_mut().unwrap() };
+    write!(result, "{:?}", *rule.read()).unwrap();
+}
+
+#[no_mangle]
 pub extern "C" fn Servo_StyleRule_GetStyle(rule: RawServoStyleRuleBorrowed) -> RawServoDeclarationBlockStrong {
     let rule = RwLock::<StyleRule>::as_arc(&rule);
     rule.read().block.clone().into_strong()
 }
 
 #[no_mangle]
 pub extern "C" fn Servo_StyleRule_SetStyle(rule: RawServoStyleRuleBorrowed,
                                            declarations: RawServoDeclarationBlockBorrowed) -> () {