--- a/layout/inspector/src/inDOMUtils.cpp
+++ b/layout/inspector/src/inDOMUtils.cpp
@@ -384,18 +384,18 @@ inDOMUtils::GetCSSPropertyNames(uint32_t
       ++propCount;                                                      \
     }                                                                   \
   PR_END_MACRO
 
   // prop is the property id we're considering; propCount is how many properties
   // we've put into props so far.
   uint32_t prop = 0, propCount = 0;
   for ( ; prop < eCSSProperty_COUNT_no_shorthands; ++prop) {
-    if (!nsCSSProps::PropHasFlags(nsCSSProperty(prop),
-                                  CSS_PROPERTY_PARSE_INACCESSIBLE)) {
+    if (nsCSSProps::PropertyParseType(nsCSSProperty(prop)) !=
+        CSS_PROPERTY_PARSE_INACCESSIBLE) {
       DO_PROP(prop);
     }
   }
 
   if (!(aFlags & EXCLUDE_SHORTHANDS)) {
     for ( ; prop < eCSSProperty_COUNT; ++prop) {
       // Some shorthands are also aliases
       if ((aFlags & INCLUDE_ALIASES) ||

--- a/layout/style/nsCSSProps.h
+++ b/layout/style/nsCSSProps.h
@@ -223,16 +223,20 @@ public:
 private:
   static const uint32_t        kFlagsTable[eCSSProperty_COUNT];
 
 public:
   static inline bool PropHasFlags(nsCSSProperty aProperty, uint32_t aFlags)
   {
     NS_ABORT_IF_FALSE(0 <= aProperty && aProperty < eCSSProperty_COUNT,
                       "out of range");
+    MOZ_ASSERT(!(aFlags & CSS_PROPERTY_PARSE_PROPERTY_MASK),
+               "The CSS_PROPERTY_PARSE_* values are not bitflags; don't pass "
+               "them to PropHasFlags.  You probably want PropertyParseType "
+               "instead.");
     return (nsCSSProps::kFlagsTable[aProperty] & aFlags) == aFlags;
   }
 
   static inline uint32_t PropertyParseType(nsCSSProperty aProperty)
   {
     NS_ABORT_IF_FALSE(0 <= aProperty && aProperty < eCSSProperty_COUNT,
                       "out of range");
     return nsCSSProps::kFlagsTable[aProperty] &