diff --git a/mozilla/modules/libpref/src/nsPref.cpp b/mozilla/modules/libpref/src/nsPref.cpp
index 444e17798c9..749b27c1fc2 100644
--- a/mozilla/modules/libpref/src/nsPref.cpp
+++ b/mozilla/modules/libpref/src/nsPref.cpp
@@ -1007,6 +1007,9 @@ PrefResult pref_OpenFileSpec(
 
     if (NS_FAILED(fileSpec->ResolveSymlink()))
       return PREF_ERROR;
+
+    if (!fileSpec->Exists())
+        return PREF_ERROR;
     
     char* readBuf;
     if (NS_FAILED(fileSpec->GetFileContents(&readBuf)))