--- a/servo/components/style/rule_tree/mod.rs
+++ b/servo/components/style/rule_tree/mod.rs
@@ -234,16 +234,27 @@ impl RuleTree {
                 }
             }
         }
 
         // Now the rule is in the relevant place, push the children as
         // necessary.
         Some(self.insert_ordered_rules_from(current, children.into_iter().rev()))
     }
+
+    /// Returns new rule nodes without Transitions level rule.
+    /// Note: this funciton supposes that rule nodes have been already ordered.
+    pub fn remove_transition_rule(&self, path: &StrongRuleNode) -> StrongRuleNode {
+        // Return a clone if there is no transition level.
+        if path.cascade_level() != CascadeLevel::Transitions {
+            return path.clone();
+        }
+
+        path.parent().unwrap().clone()
+    }
 }
 
 /// The number of RuleNodes added to the free list before we will consider
 /// doing a GC when calling maybe_gc().  (The value is copied from Gecko,
 /// where it likely did not result from a rigorous performance analysis.)
 const RULE_TREE_GC_INTERVAL: usize = 300;
 
 /// The cascade level these rules are relevant at, as per[1].