diff --git a/content/html/content/src/nsHTMLBodyElement.cpp b/content/html/content/src/nsHTMLBodyElement.cpp
index 7f0e02ac098..3d4524cf958 100644
--- a/content/html/content/src/nsHTMLBodyElement.cpp
+++ b/content/html/content/src/nsHTMLBodyElement.cpp
@@ -257,7 +257,7 @@ BodyRule::MapRuleInfoInto(nsRuleData* aData)
 BodyRule::List(FILE* out, int32_t aIndent) const
 {
   for (int32_t index = aIndent; --index >= 0; ) fputs("  ", out);
-  printf("[body rule] {}\n");
+  fputs("[body rule] {}\n", out);
 }
 #endif
 
diff --git a/layout/style/AnimationCommon.cpp b/layout/style/AnimationCommon.cpp
index bd06b43111e..bb1c56e4133 100644
--- a/layout/style/AnimationCommon.cpp
+++ b/layout/style/AnimationCommon.cpp
@@ -186,15 +186,15 @@ AnimValuesStyleRule::MapRuleInfoInto(nsRuleData* aRuleData)
 AnimValuesStyleRule::List(FILE* out, int32_t aIndent) const
 {
   for (int32_t index = aIndent; --index >= 0; ) fputs("  ", out);
-  printf("[anim values] { ");
+  fputs("[anim values] { ", out);
   for (uint32_t i = 0, i_end = mPropertyValuePairs.Length(); i < i_end; ++i) {
     const PropertyValuePair &pair = mPropertyValuePairs[i];
     nsAutoString value;
     nsStyleAnimation::UncomputeValue(pair.mProperty, pair.mValue, value);
-    printf("%s: %s; ", nsCSSProps::GetStringValue(pair.mProperty).get(),
-                       NS_ConvertUTF16toUTF8(value).get());
+    fprintf(out, "%s: %s; ", nsCSSProps::GetStringValue(pair.mProperty).get(),
+                             NS_ConvertUTF16toUTF8(value).get());
   }
-  printf("}\n");
+  fputs("}\n", out);
 }
 #endif
 
diff --git a/layout/style/nsHTMLStyleSheet.cpp b/layout/style/nsHTMLStyleSheet.cpp
index 3f03dd12450..59f241386c6 100644
--- a/layout/style/nsHTMLStyleSheet.cpp
+++ b/layout/style/nsHTMLStyleSheet.cpp
@@ -59,7 +59,7 @@ nsHTMLStyleSheet::HTMLColorRule::MapRuleInfoInto(nsRuleData* aRuleData)
 nsHTMLStyleSheet::HTMLColorRule::List(FILE* out, int32_t aIndent) const
 {
   for (int32_t index = aIndent; --index >= 0; ) fputs("  ", out);
-  printf("[html color rule] {}\n");
+  fputs("[html color rule] {}\n", out);
 }
 #endif
 
@@ -71,7 +71,7 @@ NS_IMPL_ISUPPORTS1(nsHTMLStyleSheet::GenericTableRule, nsIStyleRule)
 nsHTMLStyleSheet::GenericTableRule::List(FILE* out, int32_t aIndent) const
 {
   for (int32_t index = aIndent; --index >= 0; ) fputs("  ", out);
-  printf("[generic table rule] {}\n");
+  fputs("[generic table rule] {}\n", out);
 }
 #endif
 
diff --git a/layout/style/nsStyleSet.cpp b/layout/style/nsStyleSet.cpp
index e735ad2e307..d13890f1651 100644
--- a/layout/style/nsStyleSet.cpp
+++ b/layout/style/nsStyleSet.cpp
@@ -46,7 +46,7 @@ nsEmptyStyleRule::MapRuleInfoInto(nsRuleData* aRuleData)
 nsEmptyStyleRule::List(FILE* out, int32_t aIndent) const
 {
   for (int32_t index = aIndent; --index >= 0; ) fputs("  ", out);
-  printf("[empty style rule] {}\n");
+  fputs("[empty style rule] {}\n", out);
 }
 #endif
 
@@ -92,7 +92,7 @@ nsInitialStyleRule::MapRuleInfoInto(nsRuleData* aRuleData)
 nsInitialStyleRule::List(FILE* out, int32_t aIndent) const
 {
   for (int32_t index = aIndent; --index >= 0; ) fputs("  ", out);
-  printf("[initial style rule] {}\n");
+  fputs("[initial style rule] {}\n", out);
 }
 #endif