--- a/servo/components/style/stylist.rs
+++ b/servo/components/style/stylist.rs
@@ -793,25 +793,29 @@ impl Stylist {
         &self,
         stylesheets: I,
         guard: &SharedRwLockReadGuard
     ) -> bool
         where I: Iterator<Item = &'a Arc<Stylesheet>>
     {
         use invalidation::media_queries::PotentiallyEffectiveMediaRules;
 
+        debug!("Stylist::media_features_change_changed_style");
+
         for stylesheet in stylesheets {
             let effective_now =
                 stylesheet.media.read_with(guard)
                     .evaluate(&self.device, self.quirks_mode);
 
             let effective_then =
                 self.effective_media_query_results.was_effective(&**stylesheet);
 
             if effective_now != effective_then {
+                debug!(" > Stylesheet changed -> {}, {}",
+                       effective_then, effective_now);
                 return true
             }
 
             if !effective_now {
                 continue;
             }
 
             let mut iter =
@@ -837,31 +841,35 @@ impl Stylist {
                     CssRule::Import(ref lock) => {
                         let import_rule = lock.read_with(guard);
                         let mq = import_rule.stylesheet.media.read_with(guard);
                         let effective_now =
                             mq.evaluate(&self.device, self.quirks_mode);
                         let effective_then =
                             self.effective_media_query_results.was_effective(import_rule);
                         if effective_now != effective_then {
+                            debug!(" > @import rule changed {} -> {}",
+                                   effective_then, effective_now);
                             return true;
                         }
 
                         if !effective_now {
                             iter.skip_children();
                         }
                     }
                     CssRule::Media(ref lock) => {
                         let media_rule = lock.read_with(guard);
                         let mq = media_rule.media_queries.read_with(guard);
                         let effective_now =
                             mq.evaluate(&self.device, self.quirks_mode);
                         let effective_then =
                             self.effective_media_query_results.was_effective(media_rule);
                         if effective_now != effective_then {
+                            debug!(" > @media rule changed {} -> {}",
+                                   effective_then, effective_now);
                             return true;
                         }
 
                         if !effective_now {
                             iter.skip_children();
                         }
                     }
                 }