--- a/dom/plugins/test/testplugin/nptest.cpp
+++ b/dom/plugins/test/testplugin/nptest.cpp
@@ -689,17 +689,16 @@ NP_GetValue(void* future, NPPVariable aV
     case NPPVpluginNameString:
       *((const char**)aValue) = sPluginName;
       break;
     case NPPVpluginDescriptionString:
       *((const char**)aValue) = sPluginDescription;
       break;
     default:
       return NPERR_INVALID_PARAM;
-      break;
   }
   return NPERR_NO_ERROR;
 }
 #endif
 
 static bool fillPluginFunctionTable(NPPluginFuncs* pFuncs)
 {
   // Check the size of the provided structure based on the offset of the
@@ -2201,17 +2200,19 @@ compareVariants(NPP instance, const NPVa
   bool success = true;
   InstanceData* id = static_cast<InstanceData*>(instance->pdata);
   if (var1->type != var2->type) {
     id->err << "Variant types don't match; got " << var1->type <<
         " expected " << var2->type;
     return false;
   }
 
-  switch (var1->type) {
+  // Cast var1->type from NPVariantType to int to avoid compiler warnings about
+  // not needing a default case when we have cases for every enum value.
+  switch (static_cast<int>(var1->type)) {
     case NPVariantType_Int32: {
         int32_t result = NPVARIANT_TO_INT32(*var1);
         int32_t expected = NPVARIANT_TO_INT32(*var2);
         if (result != expected) {
           id->err << "Variant values don't match; got " << result <<
               " expected " << expected;
           success = false;
         }
@@ -2294,16 +2295,17 @@ compareVariants(NPP instance, const NPVa
           }
         }
         NPN_MemFree(identifiers);
         break;
       }
     default:
       id->err << "Unknown variant type";
       success = false;
+      MOZ_ASSERT_UNREACHABLE("Unknown variant type?!");
   }
 
   return success;
 }
 
 static bool
 throwExceptionNextInvoke(NPObject* npobj, const NPVariant* args, uint32_t argCount, NPVariant* result)
 {
@@ -3976,9 +3978,8 @@ getAudioMuted(NPObject* npobj, const NPV
     return false;
   }
 
   NPP npp = static_cast<TestNPObject*>(npobj)->npp;
   InstanceData* id = static_cast<InstanceData*>(npp->pdata);
   BOOLEAN_TO_NPVARIANT(id->audioMuted, *result);
   return true;
 }
-

--- a/dom/plugins/test/testplugin/nptest_gtk2.cpp
+++ b/dom/plugins/test/testplugin/nptest_gtk2.cpp
@@ -466,18 +466,17 @@ int32_t pluginGetEdge(InstanceData* inst
     return pluginX;
   case EDGE_TOP:
     return pluginY;
   case EDGE_RIGHT:
     return pluginX + pluginWidth;
   case EDGE_BOTTOM:
     return pluginY + pluginHeight;
   }
-
-  return NPTEST_INT32_ERROR;
+  MOZ_CRASH("Unexpected RectEdge?!");
 }
 
 #ifdef MOZ_X11
 static void intersectWithShapeRects(Display* display, Window window,
                                     int kind, GdkRegion* region)
 {
   int count = -1, order;
   XRectangle* shapeRects =

--- a/dom/plugins/test/testplugin/nptest_macosx.mm
+++ b/dom/plugins/test/testplugin/nptest_macosx.mm
@@ -270,17 +270,17 @@ int32_t pluginGetEdge(InstanceData* inst
     return w->x;
   case EDGE_TOP:
     return w->y;
   case EDGE_RIGHT:
     return w->x + w->width;
   case EDGE_BOTTOM:
     return w->y + w->height;
   }
-  return NPTEST_INT32_ERROR;
+  MOZ_CRASH("Unexpected RectEdge?!");
 }
 
 int32_t pluginGetClipRegionRectCount(InstanceData* instanceData)
 {
   return 1;
 }
 
 int32_t pluginGetClipRegionRectEdge(InstanceData* instanceData, 
@@ -299,14 +299,14 @@ int32_t pluginGetClipRegionRectEdge(Inst
     return w->clipRect.left;
   case EDGE_TOP:
     return w->clipRect.top + COCOA_TITLEBAR_HEIGHT;
   case EDGE_RIGHT:
     return w->clipRect.right;
   case EDGE_BOTTOM:
     return w->clipRect.bottom + COCOA_TITLEBAR_HEIGHT;
   }
-  return NPTEST_INT32_ERROR;
+  MOZ_CRASH("Unexpected RectEdge?!");
 }
 
 void pluginDoInternalConsistencyCheck(InstanceData* instanceData, string& error)
 {
 }