diff --git a/components/style/traversal.rs b/components/style/traversal.rs
index e4b1d8f11de..69521c1557a 100644
--- a/components/style/traversal.rs
+++ b/components/style/traversal.rs
@@ -148,7 +148,11 @@ pub trait DomTraversalContext<N: TNode>  {
     /// Process `node` on the way up, after its children have been processed.
     fn process_postorder(&self, node: N);
 
-    /// Returns if the node should be processed by the preorder traversal.
+    /// Returns if the node should be processed by the preorder traversal (and
+    /// then by the post-order one).
+    ///
+    /// Note that this is true unconditionally for servo, since it requires to
+    /// bubble the widths bottom-up for all the DOM.
     fn should_process(&self, _node: N) -> bool { true }
 
     /// Do an action over the child before pushing him to the work queue.
diff --git a/ports/geckolib/glue.rs b/ports/geckolib/glue.rs
index 95f316f5cc1..288e65431e5 100644
--- a/ports/geckolib/glue.rs
+++ b/ports/geckolib/glue.rs
@@ -113,13 +113,13 @@ fn restyle_subtree(node: GeckoNode, raw_data: *mut RawServoStyleSet) {
         timer: Timer::new(),
     };
 
-    if node.is_dirty() || node.has_dirty_descendants() {
-        if per_doc_data.num_threads == 1 {
-            sequential::traverse_dom::<GeckoNode, RecalcStyleOnly>(node, &shared_style_context);
-        } else {
-            parallel::traverse_dom::<GeckoNode, RecalcStyleOnly>(node, &shared_style_context,
-                                                                 &mut per_doc_data.work_queue);
-        }
+    // We ensure this is true before calling Servo_RestyleSubtree()
+    debug_assert!(node.is_dirty() || node.has_dirty_descendants());
+    if per_doc_data.num_threads == 1 {
+        sequential::traverse_dom::<GeckoNode, RecalcStyleOnly>(node, &shared_style_context);
+    } else {
+        parallel::traverse_dom::<GeckoNode, RecalcStyleOnly>(node, &shared_style_context,
+                                                             &mut per_doc_data.work_queue);
     }
 }
 
diff --git a/ports/geckolib/traversal.rs b/ports/geckolib/traversal.rs
index 6a3667e0b96..562153baf07 100644
--- a/ports/geckolib/traversal.rs
+++ b/ports/geckolib/traversal.rs
@@ -36,12 +36,14 @@ impl<'lc, 'ln> DomTraversalContext<GeckoNode<'ln>> for RecalcStyleOnly<'lc> {
         recalc_style_at(&self.context, self.root, node);
     }
 
+    fn process_postorder(&self, _: GeckoNode<'ln>) {}
+
+    /// In Gecko we use this traversal just for restyling, so we can stop once
+    /// we know there aren't more dirty nodes under ourselves.
     fn should_process(&self, node: GeckoNode<'ln>) -> bool {
         node.is_dirty() || node.has_dirty_descendants()
     }
 
-    fn process_postorder(&self, _: GeckoNode<'ln>) {}
-
     fn pre_process_child_hook(&self, parent: GeckoNode<'ln>, kid: GeckoNode<'ln>) {
         // NOTE: At this point is completely safe to modify either the parent or
         // the child, since we have exclusive access to them.