diff --git a/content/base/src/nsDocument.cpp b/content/base/src/nsDocument.cpp
index 5e00410ff65a..2df760bea79f 100644
--- a/content/base/src/nsDocument.cpp
+++ b/content/base/src/nsDocument.cpp
@@ -8120,7 +8120,7 @@ nsIDocument::ScheduleFrameRequestCallback(nsIFrameRequestCallback* aCallback,
   PRInt32 newHandle = ++mFrameRequestCallbackCounter;
 
   bool alreadyRegistered = !mFrameRequestCallbacks.IsEmpty();
-  FrameRequest *request =
+  DebugOnly<FrameRequest*> request =
     mFrameRequestCallbacks.AppendElement(FrameRequest(aCallback, newHandle));
   NS_ASSERTION(request, "This is supposed to be infallible!");
   if (!alreadyRegistered && mPresShell && IsEventHandlingEnabled()) {
@@ -8303,11 +8303,8 @@ nsDocument::RemoveImage(imgIRequest* aImage)
   NS_ENSURE_ARG_POINTER(aImage);
 
   // Get the old count. It should exist and be > 0.
-  PRUint32 count;
-#ifdef DEBUG
-  bool found =
-#endif
-  mImageTracker.Get(aImage, &count);
+  PRUint32 count = 0;
+  DebugOnly<bool> found = mImageTracker.Get(aImage, &count);
   NS_ABORT_IF_FALSE(found, "Removing image that wasn't in the tracker!");
   NS_ABORT_IF_FALSE(count > 0, "Entry in the cache tracker with count 0!");
 
diff --git a/content/base/src/nsFrameMessageManager.cpp b/content/base/src/nsFrameMessageManager.cpp
index 8c3c8fd81db5..62fb3f2b7df8 100644
--- a/content/base/src/nsFrameMessageManager.cpp
+++ b/content/base/src/nsFrameMessageManager.cpp
@@ -349,7 +349,8 @@ class MMListenerRemover
 {
 public:
   MMListenerRemover(nsFrameMessageManager* aMM)
-  : mMM(aMM), mWasHandlingMessage(aMM->mHandlingMessage)
+    : mWasHandlingMessage(aMM->mHandlingMessage)
+    , mMM(aMM)
   {
     mMM->mHandlingMessage = true;
   }
diff --git a/content/media/nsBuiltinDecoder.cpp b/content/media/nsBuiltinDecoder.cpp
index a0f40e5802f3..ba261462c5ea 100644
--- a/content/media/nsBuiltinDecoder.cpp
+++ b/content/media/nsBuiltinDecoder.cpp
@@ -327,7 +327,9 @@ nsresult nsBuiltinDecoder::Seek(double aTime)
   PRInt32 range = 0;
   if (!IsInRanges(seekable, aTime, range)) {
     if (range != -1) {
-      if (range + 1 < length) {
+      // |range + 1| can't be negative, because the only possible negative value
+      // for |range| is -1.
+      if (PRUint32(range + 1) < length) {
         double leftBound, rightBound;
         res = seekable.End(range, &leftBound);
         NS_ENSURE_SUCCESS(res, NS_OK);
diff --git a/content/media/nsBuiltinDecoderStateMachine.cpp b/content/media/nsBuiltinDecoderStateMachine.cpp
index 6650862289fb..8f03e5881bcd 100644
--- a/content/media/nsBuiltinDecoderStateMachine.cpp
+++ b/content/media/nsBuiltinDecoderStateMachine.cpp
@@ -49,6 +49,7 @@
 
 #include "mozilla/Preferences.h"
 #include "mozilla/StdInt.h"
+#include "mozilla/Util.h"
 
 using namespace mozilla;
 using namespace mozilla::layers;
@@ -307,9 +308,8 @@ void StateMachineTracker::EnsureGlobalStateMachine()
   ReentrantMonitorAutoEnter mon(mMonitor);
   if (mStateMachineCount == 0) {
     NS_ASSERTION(!mStateMachineThread, "Should have null state machine thread!");
-    nsresult res = NS_NewThread(&mStateMachineThread,
-                                nsnull);
-    NS_ABORT_IF_FALSE(NS_SUCCEEDED(res), "Can't create media state machine thread");
+    DebugOnly<nsresult> rv = NS_NewThread(&mStateMachineThread, nsnull);
+    NS_ABORT_IF_FALSE(NS_SUCCEEDED(rv), "Can't create media state machine thread");
   }
   mStateMachineCount++;
 }
@@ -866,11 +866,11 @@ void nsBuiltinDecoderStateMachine::AudioLoop()
       ReentrantMonitorAutoEnter mon(mDecoder->GetReentrantMonitor());
       PRInt64 unplayedFrames = audioDuration % minWriteFrames;
       if (minWriteFrames > 1 && unplayedFrames > 0) {
-        // Sound is written by libsydneyaudio to the hardware in blocks of
-        // frames of size minWriteFrames. So if the number of frames we've
-        // written isn't an exact multiple of minWriteFrames, we'll have
-        // left over audio data which hasn't yet been written to the hardware,
-        // and so that audio will not start playing. Write silence to ensure
+        // Sound is written by libsydneyaudio to the hardware in blocks of
+        // frames of size minWriteFrames. So if the number of frames we've
+        // written isn't an exact multiple of minWriteFrames, we'll have
+        // left over audio data which hasn't yet been written to the hardware,
+        // and so that audio will not start playing. Write silence to ensure
         // the last block gets pushed to hardware, so that playback starts.
         PRInt64 framesToWrite = minWriteFrames - unplayedFrames;
         if (framesToWrite < PR_UINT32_MAX / channels) {