--- a/xpcom/glue/nsID.cpp
+++ b/xpcom/glue/nsID.cpp
@@ -8,19 +8,17 @@
 #include "nsMemory.h"
 #include "mozilla/Sprintf.h"
 
 void nsID::Clear()
 {
   m0 = 0;
   m1 = 0;
   m2 = 0;
-  for (int i = 0; i < 8; ++i) {
-    m3[i] = 0;
-  }
+  memset(m3, 0, sizeof(m3));
 }
 
 /**
  * Multiplies the_int_var with 16 (0x10) and adds the value of the
  * hexadecimal digit the_char. If it fails it returns false from
  * the function it's used in.
  */
 

--- a/xpcom/io/nsLocalFileUnix.cpp
+++ b/xpcom/io/nsLocalFileUnix.cpp
@@ -1552,18 +1552,18 @@ nsLocalFile::IsExecutable(bool* aResult)
     }
 
     // Search for any of the set of executable extensions.
     static const char* const executableExts[] = {
       "air",  // Adobe AIR installer
       "jar"   // java application bundle
     };
     nsDependentSubstring ext = Substring(path, dotIdx + 1);
-    for (size_t i = 0; i < ArrayLength(executableExts); i++) {
-      if (ext.EqualsASCII(executableExts[i])) {
+    for (auto executableExt : executableExts) {
+      if (ext.EqualsASCII(executableExt)) {
         // Found a match.  Set result and quit.
         *aResult = true;
         return NS_OK;
       }
     }
   }
 
   // On OS X, then query Launch Services.

--- a/xpcom/tests/gtest/TestHashtables.cpp
+++ b/xpcom/tests/gtest/TestHashtables.cpp
@@ -279,24 +279,24 @@ TEST(Hashtable, THashtable)
   ASSERT_EQ(count, uint32_t(0));
 }
 
 TEST(Hashtables, DataHashtable)
 {
   // check a data-hashtable
   nsDataHashtable<nsUint32HashKey,const char*> UniToEntity(ENTITY_COUNT);
 
-  for (uint32_t i = 0; i < ENTITY_COUNT; ++i) {
-    UniToEntity.Put(gEntities[i].mUnicode, gEntities[i].mStr);
+  for (auto& entity : gEntities) {
+    UniToEntity.Put(entity.mUnicode, entity.mStr);
   }
 
   const char* str;
 
-  for (uint32_t i = 0; i < ENTITY_COUNT; ++i) {
-    ASSERT_TRUE(UniToEntity.Get(gEntities[i].mUnicode, &str));
+  for (auto& entity : gEntities) {
+    ASSERT_TRUE(UniToEntity.Get(entity.mUnicode, &str));
   }
 
   ASSERT_FALSE(UniToEntity.Get(99446, &str));
 
   uint32_t count = 0;
   for (auto iter = UniToEntity.Iter(); !iter.Done(); iter.Next()) {
     count++;
   }
@@ -312,25 +312,25 @@ TEST(Hashtables, DataHashtable)
   ASSERT_EQ(count, uint32_t(0));
 }
 
 TEST(Hashtables, ClassHashtable)
 {
   // check a class-hashtable
   nsClassHashtable<nsCStringHashKey,TestUniChar> EntToUniClass(ENTITY_COUNT);
 
-  for (uint32_t i = 0; i < ENTITY_COUNT; ++i) {
-    TestUniChar* temp = new TestUniChar(gEntities[i].mUnicode);
-    EntToUniClass.Put(nsDependentCString(gEntities[i].mStr), temp);
+  for (auto& entity : gEntities) {
+    TestUniChar* temp = new TestUniChar(entity.mUnicode);
+    EntToUniClass.Put(nsDependentCString(entity.mStr), temp);
   }
 
   TestUniChar* myChar;
 
-  for (uint32_t i = 0; i < ENTITY_COUNT; ++i) {
-    ASSERT_TRUE(EntToUniClass.Get(nsDependentCString(gEntities[i].mStr), &myChar));
+  for (auto& entity : gEntities) {
+    ASSERT_TRUE(EntToUniClass.Get(nsDependentCString(entity.mStr), &myChar));
   }
 
   ASSERT_FALSE(EntToUniClass.Get(NS_LITERAL_CSTRING("xxxx"), &myChar));
 
   uint32_t count = 0;
   for (auto iter = EntToUniClass.Iter(); !iter.Done(); iter.Next()) {
     count++;
   }
@@ -391,27 +391,27 @@ TEST(Hashtables, DataHashtableWithInterf
   ASSERT_EQ(count, uint32_t(0));
 }
 
 TEST(Hashtables, InterfaceHashtable)
 {
   // check an interface-hashtable with an uint32_t key
   nsInterfaceHashtable<nsUint32HashKey,IFoo> UniToEntClass2(ENTITY_COUNT);
 
-  for (uint32_t i = 0; i < ENTITY_COUNT; ++i) {
+  for (auto& entity : gEntities) {
     nsCOMPtr<IFoo> foo;
     CreateIFoo(getter_AddRefs(foo));
-    foo->SetString(nsDependentCString(gEntities[i].mStr));
+    foo->SetString(nsDependentCString(entity.mStr));
 
-    UniToEntClass2.Put(gEntities[i].mUnicode, foo);
+    UniToEntClass2.Put(entity.mUnicode, foo);
   }
 
-  for (uint32_t i = 0; i < ENTITY_COUNT; ++i) {
+  for (auto& entity : gEntities) {
     nsCOMPtr<IFoo> myEnt;
-    ASSERT_TRUE(UniToEntClass2.Get(gEntities[i].mUnicode, getter_AddRefs(myEnt)));
+    ASSERT_TRUE(UniToEntClass2.Get(entity.mUnicode, getter_AddRefs(myEnt)));
 
     nsAutoCString myEntStr;
     myEnt->GetString(myEntStr);
   }
 
   nsCOMPtr<IFoo> myEnt;
   ASSERT_FALSE(UniToEntClass2.Get(9462, getter_AddRefs(myEnt)));