diff --git a/config/createprecomplete.py b/config/createprecomplete.py
index 560677623e42..3241d526b281 100644
--- a/config/createprecomplete.py
+++ b/config/createprecomplete.py
@@ -44,14 +44,17 @@ def generate_precomplete(root_path):
         application update instructions. The given directory is used
         for the location to enumerate and to create the precomplete file.
     """
+    rel_path_precomplete = "precomplete"
     # If inside a Mac bundle use the root of the bundle for the path.
     if os.path.basename(root_path) == "Resources":
         root_path = os.path.abspath(os.path.join(root_path, '../../'))
+        rel_path_precomplete = "Contents/Resources/precomplete"
 
-    rel_file_path_list, rel_dir_path_list = get_build_entries(root_path)
-    precomplete_file_path = os.path.join(root_path,"precomplete")
-    # open in binary mode to prevent OS specific line endings.
+    precomplete_file_path = os.path.join(root_path,rel_path_precomplete)
+    # Open the file so it exists before building the list of files and open it
+    # in binary mode to prevent OS specific line endings.
     precomplete_file = open(precomplete_file_path, "wb")
+    rel_file_path_list, rel_dir_path_list = get_build_entries(root_path)
     for rel_file_path in rel_file_path_list:
         precomplete_file.writelines("remove \""+rel_file_path+"\"\n")
 
diff --git a/toolkit/mozapps/update/updater/updater.cpp b/toolkit/mozapps/update/updater/updater.cpp
index ce6af32b9f3b..8a6e107545a5 100644
--- a/toolkit/mozapps/update/updater/updater.cpp
+++ b/toolkit/mozapps/update/updater/updater.cpp
@@ -2090,43 +2090,8 @@ ProcessReplaceRequest()
     LOG(("Updated.app dir can't be found: " LOG_S ", err: %d",
          updatedAppDir, errno));
   }
+
   ensure_remove_recursive(updatedAppDir);
-
-  LOG(("Moving the precomplete file"));
-
-  // We also need to move the precomplete file too.
-  NS_tchar precompleteSource[MAXPATHLEN];
-  NS_tsnprintf(precompleteSource, sizeof(precompleteSource)/sizeof(precompleteSource[0]),
-               NS_T("%s/precomplete"), installDir);
-
-  NS_tchar precompleteTmp[MAXPATHLEN];
-  NS_tsnprintf(precompleteTmp, sizeof(precompleteTmp)/sizeof(precompleteTmp[0]),
-               NS_T("%s/precomplete.bak"), installDir);
-
-  NS_tchar precompleteNew[MAXPATHLEN];
-  NS_tsnprintf(precompleteNew, sizeof(precompleteNew)/sizeof(precompleteNew[0]),
-               NS_T("%s/Updated.app/precomplete"), installDir);
-
-  ensure_remove(precompleteTmp);
-  LOG(("Begin moving precompleteSrc to precompleteTmp"));
-  rv = rename_file(precompleteSource, precompleteTmp);
-  LOG(("Moved precompleteSrc to precompleteTmp, err: %d", rv));
-  LOG(("Begin moving precompleteNew to precompleteSrc"));
-  int rv2 = rename_file(precompleteNew, precompleteSource);
-  LOG(("Moved precompleteNew to precompleteSrc, err: %d", rv2));
-
-  // If new could not be moved to source, we only want to restore tmp to source
-  // if the first step succeeded.  Note that it is possible for the first
-  // rename to have failed as well, for example if the tmpFile exists and we
-  // race between the ensure_remove call and the first rename call, but there
-  // isn't too much that we can do about that, unfortunately.
-  if (!rv && rv2) {
-    LOG(("Begin trying to recover precompleteSrc"));
-    rv = rename_file(precompleteTmp, precompleteSource);
-    LOG(("Moved precompleteTmp to precompleteSrc, err: %d", rv));
-  }
-
-  LOG(("Finished moving the precomplete file"));
 #endif
 
   gSucceeded = true;
@@ -3639,7 +3604,11 @@ int AddPreCompleteActions(ActionList *list)
     return OK;
   }
 
+#ifdef XP_MACOSX
+  NS_tchar *rb = GetManifestContents(NS_T("Contents/Resources/precomplete"));
+#else
   NS_tchar *rb = GetManifestContents(NS_T("precomplete"));
+#endif
   if (rb == nullptr) {
     LOG(("AddPreCompleteActions: error getting contents of precomplete " \
          "manifest"));
diff --git a/tools/update-packaging/make_full_update.sh b/tools/update-packaging/make_full_update.sh
index 0ab09a6746c9..f0466144dfc6 100755
--- a/tools/update-packaging/make_full_update.sh
+++ b/tools/update-packaging/make_full_update.sh
@@ -49,9 +49,6 @@ targetfiles="updatev2.manifest updatev3.manifest"
 
 mkdir -p "$workdir"
 
-# On Mac, the precomplete file added by Bug 386760 will cause OS X to reload the
-# Info.plist so it launches the right architecture, bug 600098
-
 # Generate a list of all files in the target directory.
 pushd "$targetdir"
 if test $? -ne 0 ; then
@@ -59,8 +56,10 @@ if test $? -ne 0 ; then
 fi
 
 if [ ! -f "precomplete" ]; then
-  notice "precomplete file is missing!"
-  exit 1
+  if [ ! -f "Contents/Resources/precomplete" ]; then
+    notice "precomplete file is missing!"
+    exit 1
+  fi
 fi
 
 list_files files
diff --git a/tools/update-packaging/make_incremental_update.sh b/tools/update-packaging/make_incremental_update.sh
index 507627b8fd8d..cd170cd0dbd8 100755
--- a/tools/update-packaging/make_incremental_update.sh
+++ b/tools/update-packaging/make_incremental_update.sh
@@ -35,6 +35,11 @@ check_for_forced_update() {
     return 0;
   fi
 
+  if [ "$forced_file_chk" = "Contents/Resources/precomplete" ]; then
+    ## "true" *giggle*
+    return 0;
+  fi
+
   if [ "${forced_file_chk##*.}" = "chk" ]
   then
     ## "true" *giggle*
@@ -92,9 +97,6 @@ archivefiles="updatev2.manifest updatev3.manifest"
 
 mkdir -p "$workdir"
 
-# On Mac, the precomplete file added by Bug 386760 will cause OS X to reload the
-# Info.plist so it launches the right architecture, bug 600098
-
 # Generate a list of all files in the target directory.
 pushd "$olddir"
 if test $? -ne 0 ; then
@@ -112,8 +114,10 @@ if test $? -ne 0 ; then
 fi
 
 if [ ! -f "precomplete" ]; then
-  notice "precomplete file is missing!"
-  exit 1
+  if [ ! -f "Contents/Resources/precomplete" ]; then
+    notice "precomplete file is missing!"
+    exit 1
+  fi
 fi
 
 list_dirs newdirs
diff --git a/tools/update-packaging/make_incremental_updates.py b/tools/update-packaging/make_incremental_updates.py
index b06904a66811..0867434aeaf4 100755
--- a/tools/update-packaging/make_incremental_updates.py
+++ b/tools/update-packaging/make_incremental_updates.py
@@ -336,12 +336,20 @@ def create_partial_patch(from_dir_path, to_dir_path, patch_filename, shas, patch
     # Create a hashtable of the from  and to directories
     from_dir_hash,from_file_set,from_dir_set = patch_info.build_marfile_entry_hash(from_dir_path)
     to_dir_hash,to_file_set,to_dir_set = patch_info.build_marfile_entry_hash(to_dir_path)
-    # Require that the precomplete file is included in the complete update
-    if "precomplete" not in to_file_set:
-        raise Exception, "missing precomplete file in: "+to_dir_path
     # Create a list of the forced updates 
     forced_list = forced_updates.strip().split('|')
-    forced_list.append("precomplete")
+    # Require that the precomplete file is included in the complete update
+    if "precomplete" not in to_file_set:
+        # The check with \ file separators allows tests for Mac to run on Windows
+        if "Contents/Resources/precomplete" not in to_file_set and "Contents\Resources\precomplete" not in to_file_set:
+            raise Exception, "missing precomplete file in: "+to_dir_path
+        else:
+            if "Contents/Resources/precomplete" in to_file_set:
+                forced_list.append("Contents/Resources/precomplete")
+            else:
+                forced_list.append("Contents\Resources\precomplete")
+    else:
+        forced_list.append("precomplete")
 
     # Files which exist in both sets need to be patched
     patch_filenames = list(from_file_set.intersection(to_file_set))
diff --git a/tools/update-packaging/test/from-mac/precomplete b/tools/update-packaging/test/from-mac/Contents/Resources/precomplete
similarity index 93%
rename from tools/update-packaging/test/from-mac/precomplete
rename to tools/update-packaging/test/from-mac/Contents/Resources/precomplete
index 5dd59ea913e9..2d9068d3723b 100644
--- a/tools/update-packaging/test/from-mac/precomplete
+++ b/tools/update-packaging/test/from-mac/Contents/Resources/precomplete
@@ -1,4 +1,3 @@
-remove "precomplete"
 remove "Contents/MacOS/{foodir/update.manifest"
 remove "Contents/MacOS/{foodir/same.txt"
 remove "Contents/MacOS/{foodir/same.bin"
@@ -16,10 +15,12 @@ remove "Contents/MacOS/force.txt"
 remove "Contents/MacOS/extensions/diff/diff-patch-larger-than-file.txt"
 remove "Contents/MacOS/diff-patch-larger-than-file.txt"
 remove "Contents/MacOS/application.ini"
+remove "Contents/Resources/precomplete"
 rmdir "Contents/MacOS/{foodir/"
 rmdir "Contents/MacOS/searchplugins/diff/"
 rmdir "Contents/MacOS/searchplugins/"
 rmdir "Contents/MacOS/extensions/diff/"
 rmdir "Contents/MacOS/extensions/"
 rmdir "Contents/MacOS/"
+rmdir "Contents/Resources/"
 rmdir "Contents/"
diff --git a/tools/update-packaging/test/make_full_update.sh b/tools/update-packaging/test/make_full_update.sh
index 84d997312913..f2907da9ee47 100755
--- a/tools/update-packaging/test/make_full_update.sh
+++ b/tools/update-packaging/test/make_full_update.sh
@@ -50,9 +50,6 @@ targetfiles="updatev2.manifest updatev3.manifest"
 
 mkdir -p "$workdir"
 
-# On Mac, the precomplete file added by Bug 386760 will cause OS X to reload the
-# Info.plist so it launches the right architecture, bug 600098
-
 # Generate a list of all files in the target directory.
 pushd "$targetdir"
 if test $? -ne 0 ; then
@@ -60,8 +57,10 @@ if test $? -ne 0 ; then
 fi
 
 if [ ! -f "precomplete" ]; then
-  notice "precomplete file is missing!"
-  exit 1
+  if [ ! -f "Contents/Resources/precomplete" ]; then
+    notice "precomplete file is missing!"
+    exit 1
+  fi
 fi
 
 list_files files
diff --git a/tools/update-packaging/test/to-mac/Contents/MacOS/precomplete b/tools/update-packaging/test/to-mac/Contents/MacOS/precomplete
deleted file mode 100644
index dd64d4d6f27b..000000000000
--- a/tools/update-packaging/test/to-mac/Contents/MacOS/precomplete
+++ /dev/null
@@ -1,19 +0,0 @@
-remove "Contents/MacOS/{foodir/update.manifest"
-remove "Contents/MacOS/{foodir/same.txt"
-remove "Contents/MacOS/{foodir/same.bin"
-remove "Contents/MacOS/{foodir/readme.txt"
-remove "Contents/MacOS/{foodir/force.txt"
-remove "Contents/MacOS/{foodir/diff-patch-larger-than-file.txt"
-remove "Contents/MacOS/update.manifest"
-remove "Contents/MacOS/searchplugins/diff/diff-patch-larger-than-file.txt"
-remove "Contents/MacOS/same.txt"
-remove "Contents/MacOS/same.bin"
-remove "Contents/MacOS/removed-files"
-remove "Contents/MacOS/readme.txt"
-remove "Contents/MacOS/precomplete"
-remove "Contents/MacOS/force.txt"
-remove "Contents/MacOS/diff-patch-larger-than-file.txt"
-rmdir "Contents/MacOS/{foodir/"
-rmdir "Contents/MacOS/searchplugins/diff/"
-rmdir "Contents/MacOS/searchplugins/added/"
-rmdir "Contents/MacOS/searchplugins/"
diff --git a/tools/update-packaging/test/to-mac/precomplete b/tools/update-packaging/test/to-mac/Contents/Resources/precomplete
similarity index 95%
rename from tools/update-packaging/test/to-mac/precomplete
rename to tools/update-packaging/test/to-mac/Contents/Resources/precomplete
index 0549035754a3..7af8bfd76953 100644
--- a/tools/update-packaging/test/to-mac/precomplete
+++ b/tools/update-packaging/test/to-mac/Contents/Resources/precomplete
@@ -1,4 +1,3 @@
-remove "precomplete"
 remove "Contents/MacOS/{foodir/update.manifest"
 remove "Contents/MacOS/{foodir/same.txt"
 remove "Contents/MacOS/{foodir/same.bin"
@@ -13,7 +12,6 @@ remove "Contents/MacOS/same.txt"
 remove "Contents/MacOS/same.bin"
 remove "Contents/MacOS/removed-files"
 remove "Contents/MacOS/readme.txt"
-remove "Contents/MacOS/precomplete"
 remove "Contents/MacOS/force.txt"
 remove "Contents/MacOS/extensions/diff/diff-patch-larger-than-file.txt"
 remove "Contents/MacOS/extensions/added/file.txt"
@@ -22,6 +20,7 @@ remove "Contents/MacOS/diff-patch-larger-than-file.bin"
 remove "Contents/MacOS/application.ini"
 remove "Contents/MacOS/added.txt"
 remove "Contents/MacOS/addFeedPrefs.js"
+remove "Contents/Resources/precomplete"
 rmdir "Contents/MacOS/{foodir/"
 rmdir "Contents/MacOS/searchplugins/diff/"
 rmdir "Contents/MacOS/searchplugins/added/"
@@ -30,4 +29,5 @@ rmdir "Contents/MacOS/extensions/diff/"
 rmdir "Contents/MacOS/extensions/added/"
 rmdir "Contents/MacOS/extensions/"
 rmdir "Contents/MacOS/"
+rmdir "Contents/Resources/"
 rmdir "Contents/"