--- a/xpcom/reflect/xptinfo/xptcodegen.py
+++ b/xpcom/reflect/xptinfo/xptcodegen.py
@@ -9,19 +9,19 @@
 # reference to them.
 
 import json
 from perfecthash import PerfectHash
 import time
 from collections import OrderedDict
 
 # We fix the number of entries in our intermediate table used by the perfect
-# hashes to 256. This number is constant in xptinfo, allowing the compiler to
+# hashes to 512. This number is constant in xptinfo, allowing the compiler to
 # generate a more efficient modulo due to it being a power of 2.
-PHFSIZE = 256
+PHFSIZE = 512
 
 def indented(s):
     return s.replace('\n', '\n  ')
 
 def cpp(v):
     if type(v) == bool:
         return "true" if v else "false"
     return str(v)

--- a/xpcom/reflect/xptinfo/xptinfo.cpp
+++ b/xpcom/reflect/xptinfo/xptinfo.cpp
@@ -36,17 +36,17 @@ static uint16_t
 Phf_DoLookup(const void* aBytes, uint32_t aLen, const uint32_t* aIntr)
 {
   uint32_t mid = aIntr[Phf_DoHash(aBytes, aLen) % kPHFSize];
   if (mid & U32_HIGH_BIT) {
     return mid & ~U32_HIGH_BIT;
   }
   return Phf_DoHash(aBytes, aLen, mid) % sInterfacesSize;
 }
-static_assert(kPHFSize == 256, "wrong phf size?");
+static_assert(kPHFSize == 512, "wrong phf size?");
 
 
 ////////////////////////////////////////
 // PHF-based interface lookup methods //
 ////////////////////////////////////////
 
 /* static */ const nsXPTInterfaceInfo*
 nsXPTInterfaceInfo::ByIID(const nsIID& aIID)

--- a/xpcom/reflect/xptinfo/xptinfo.h
+++ b/xpcom/reflect/xptinfo/xptinfo.h
@@ -505,17 +505,17 @@ extern const nsXPTDOMObjectInfo sDOMObje
 
 extern const char sStrings[];
 extern const ConstInfo sConsts[];
 
 // shim constant information
 extern const mozilla::dom::NativePropertyHooks* sPropHooks[];
 
 // Perfect Hash Function backing data
-static const uint16_t kPHFSize = 256;
+static const uint16_t kPHFSize = 512;
 extern const uint32_t sPHF_IIDs[]; // Length == kPHFSize
 extern const uint32_t sPHF_Names[]; // Length == kPHFSize
 extern const uint16_t sPHF_NamesIdxs[]; // Length == sInterfacesSize
 
 
 //////////////////////////////////////
 // Helper Methods for fetching data //
 //////////////////////////////////////