--- a/dom/media/gmp-plugin/gmp-test-decryptor.cpp
+++ b/dom/media/gmp-plugin/gmp-test-decryptor.cpp
@@ -171,17 +171,17 @@ private:
 };
 
 class TestEmptyContinuation : public ReadContinuation {
 public:
   TestEmptyContinuation(TestManager* aTestManager, const string& aTestID)
     : mTestmanager(aTestManager), mTestID(aTestID) {}
 
   void ReadComplete(GMPErr aErr, const std::string& aData) override {
-    if (aData != "") {
+    if (!aData.empty()) {
       FakeDecryptor::Message("FAIL TestEmptyContinuation record was not truncated");
     }
     mTestmanager->EndTest(mTestID);
     delete this;
   }
 
 private:
   TestManager* const mTestmanager;

--- a/dom/media/gmp-plugin/gmp-test-storage.cpp
+++ b/dom/media/gmp-plugin/gmp-test-storage.cpp
@@ -20,17 +20,17 @@ public:
     mOnSuccess = aOnSuccess;
     mOnFailure = aOnFailure;
     mData.insert(mData.end(), aData, aData + aDataSize);
     return mRecord->Open();
   }
 
   void OpenComplete(GMPErr aStatus) override {
     if (GMP_SUCCEEDED(aStatus)) {
-      mRecord->Write(mData.size() ? &mData.front() : nullptr, mData.size());
+      mRecord->Write(mData.empty() ? nullptr : &mData.front(), mData.size());
     } else {
       GMPRunOnMainThread(mOnFailure);
       mOnSuccess->Destroy();
     }
   }
 
   void ReadComplete(GMPErr aStatus,
                     const uint8_t* aData,

--- a/dom/media/systemservices/MediaSystemResourceService.cpp
+++ b/dom/media/systemservices/MediaSystemResourceService.cpp
@@ -220,17 +220,17 @@ MediaSystemResourceService::UpdateReques
   }
 
   std::deque<MediaSystemResourceRequest>& acquiredRequests =
     resource->mAcquiredRequests;
   std::deque<MediaSystemResourceRequest>& waitingRequests =
     resource->mWaitingRequests;
 
   while ((acquiredRequests.size() < resource->mResourceCount) &&
-         (waitingRequests.size() > 0)) {
+         (!waitingRequests.empty())) {
     MediaSystemResourceRequest& request = waitingRequests.front();
     MOZ_ASSERT(request.mParent);
     // Send response
     mozilla::Unused << request.mParent->SendResponse(request.mId, true /* success */);
     // Move request to mAcquiredRequests
     acquiredRequests.push_back(waitingRequests.front());
     waitingRequests.pop_front();
   }

--- a/media/gmp-clearkey/0.1/ClearKeyDecryptionManager.cpp
+++ b/media/gmp-clearkey/0.1/ClearKeyDecryptionManager.cpp
@@ -33,17 +33,17 @@ bool AllZero(const std::vector<uint32_t>
 }
 
 class ClearKeyDecryptor : public RefCounted
 {
 public:
   ClearKeyDecryptor();
 
   void InitKey(const Key& aKey);
-  bool HasKey() const { return !!mKey.size(); }
+  bool HasKey() const { return !mKey.empty(); }
 
   Status Decrypt(uint8_t* aBuffer, uint32_t aBufferSize,
                  const CryptoMetaData& aMetadata);
 
   const Key& DecryptionKey() const { return mKey; }
 
 private:
   ~ClearKeyDecryptor();

--- a/media/gmp-clearkey/0.1/ClearKeySession.cpp
+++ b/media/gmp-clearkey/0.1/ClearKeySession.cpp
@@ -55,17 +55,17 @@ ClearKeySession::Init(InitDataType aInit
   } else if (aInitDataType == InitDataType::kWebM &&
              aInitDataSize <= kMaxWebmInitDataSize) {
     // "webm" initData format is simply the raw bytes of the keyId.
     vector<uint8_t> keyId;
     keyId.assign(aInitData, aInitData+aInitDataSize);
     mKeyIds.push_back(keyId);
   }
 
-  if (!mKeyIds.size()) {
+  if (mKeyIds.empty()) {
     return false;
   }
 
   return true;
 }
 
 SessionType
 ClearKeySession::Type() const