diff --git a/content/base/src/nsContentUtils.cpp b/content/base/src/nsContentUtils.cpp
index 16af08c07487..2ce689841248 100644
--- a/content/base/src/nsContentUtils.cpp
+++ b/content/base/src/nsContentUtils.cpp
@@ -4379,7 +4379,8 @@ nsIPrincipal*
 nsContentUtils::GetSystemPrincipal()
 {
   nsCOMPtr<nsIPrincipal> sysPrin;
-  nsresult rv = sSecurityManager->GetSystemPrincipal(getter_AddRefs(sysPrin));
+  DebugOnly<nsresult> rv =
+    sSecurityManager->GetSystemPrincipal(getter_AddRefs(sysPrin));
   MOZ_ASSERT(NS_SUCCEEDED(rv) && sysPrin);
   return sysPrin;
 }
diff --git a/content/base/src/nsNodeInfoManager.cpp b/content/base/src/nsNodeInfoManager.cpp
index 183a10c5e916..9638cf546441 100644
--- a/content/base/src/nsNodeInfoManager.cpp
+++ b/content/base/src/nsNodeInfoManager.cpp
@@ -9,6 +9,8 @@
  */
 
 #include "nsNodeInfoManager.h"
+
+#include "mozilla/DebugOnly.h"
 #include "nsNodeInfo.h"
 #include "nsCOMPtr.h"
 #include "nsString.h"
@@ -252,8 +254,8 @@ nsNodeInfoManager::GetNodeInfo(nsIAtom *aName, nsIAtom *aPrefix,
   nsRefPtr<nsNodeInfo> newNodeInfo =
     new nsNodeInfo(aName, aPrefix, aNamespaceID, aNodeType, aExtraName, this);
 
-  PLHashEntry *he;
-  he = PL_HashTableAdd(mNodeInfoHash, &newNodeInfo->mInner, newNodeInfo);
+  DebugOnly<PLHashEntry*> he =
+    PL_HashTableAdd(mNodeInfoHash, &newNodeInfo->mInner, newNodeInfo);
   MOZ_ASSERT(he, "PL_HashTableAdd() failed");
 
   // Have to do the swap thing, because already_AddRefed<nsNodeInfo>
diff --git a/content/base/src/nsObjectLoadingContent.cpp b/content/base/src/nsObjectLoadingContent.cpp
index 8e79aa1e5638..f12292dafaa6 100644
--- a/content/base/src/nsObjectLoadingContent.cpp
+++ b/content/base/src/nsObjectLoadingContent.cpp
@@ -3347,7 +3347,7 @@ nsObjectLoadingContent::TeardownProtoChain()
 
   // Loop over the DOM element's JS object prototype chain and remove
   // all JS objects of the class sNPObjectJSWrapperClass
-  bool removed = false;
+  DebugOnly<bool> removed = false;
   while (obj) {
     if (!::JS_GetPrototype(cx, obj, &proto)) {
       return;