diff --git a/ipc/ipdl/Makefile.in b/ipc/ipdl/Makefile.in
index 7bc05ec8a86..c42899f70af 100644
--- a/ipc/ipdl/Makefile.in
+++ b/ipc/ipdl/Makefile.in
@@ -112,19 +112,15 @@ include $(topsrcdir)/config/config.mk
 include $(topsrcdir)/ipc/chromium/chromium-config.mk
 include $(topsrcdir)/config/rules.mk
 
--include $(ALL_IPDLSRCS:.ipdl=.ipdl.depends)
 
 # NB: the IPDL compiler manages .ipdl-->.h/.cpp dependencies itself,
 # which is why we don't have explicit .h/.cpp targets here
-export:: $(CPPSRCS)
-
-$(CPPSRCS) : $(ALL_IPDLSRCS)
+export:: $(ALL_IPDLSRCS)
 	$(PYTHON) $(topsrcdir)/config/pythonpath.py	\
 	  -I$(topsrcdir)/other-licenses/ply		\
 	  $(srcdir)/ipdl.py				\
 	  --outheaders-dir=_ipdlheaders			\
 	  --outcpp-dir=.				\
-	  --dependencies				\
 	  $(IPDLDIRS:%=-I$(topsrcdir)/%)		\
 	  $^
 
diff --git a/ipc/ipdl/ipdl.py b/ipc/ipdl/ipdl.py
index 27dd461791c..e47cd108a3d 100755
--- a/ipc/ipdl/ipdl.py
+++ b/ipc/ipdl/ipdl.py
@@ -59,15 +59,12 @@ op.add_option('-o', '--outcpp-dir', dest='cppdir', default='.',
 A protocol Foo in the namespace bar will cause the sources
   cppdir/FooParent.cpp, cppdir/FooChild.cpp
 to be generated""")
-op.add_option('-m', '--dependencies', dest='emitdependencies', default=False, action='store_true',
-              help="Emit Makefile dependencies for incremental rebuilds")
 
 
 options, files = op.parse_args()
 _verbosity = options.verbosity
 headersdir = options.headersdir
 cppdir = options.cppdir
-emitdependencies = options.emitdependencies
 includedirs = [ os.path.abspath(incdir) for incdir in options.includedirs ]
 
 if not len(files):
@@ -109,16 +106,13 @@ for f in files:
         log(3, '  pretty printed code:')
         ipdl.genipdl(ast, codedir)
 
-    if emitdependencies == 1:
-        ipdl.genm(ast, cppdir, normalizedFilename(f))
-
 # Second pass: generate code
 for f in files:
     # Read from parser cache
     filename = normalizedFilename(f)
     ast = ipdl.parse(None, filename, includedirs=includedirs)
     ipdl.gencxx(filename, ast, headersdir, cppdir)
-
+    
     allprotocols.append('%sMsgStart' % ast.protocol.name)
 
 allprotocols.sort()
@@ -146,5 +140,5 @@ COMPILE_ASSERT(LastMsgIndex <= 65536, need_to_update_IPC_MESSAGE_MACRO);
 #endif // ifndef IPCMessageStart_h
 """
 
-ipdl.writetofile(ipcmsgstart.getvalue(),
+ipdl.writeifmodified(ipcmsgstart.getvalue(),
                      os.path.join(headersdir, 'IPCMessageStart.h'))
diff --git a/ipc/ipdl/ipdl/__init__.py b/ipc/ipdl/ipdl/__init__.py
index db3f253de9a..fa0cc7bf4ff 100644
--- a/ipc/ipdl/ipdl/__init__.py
+++ b/ipc/ipdl/ipdl/__init__.py
@@ -30,13 +30,12 @@
 #
 # ***** END LICENSE BLOCK *****
 
-__all__ = [ 'gencxx', 'genipdl', 'parse', 'typecheck', 'writetofile' ]
+__all__ = [ 'gencxx', 'genipdl', 'parse', 'typecheck', 'writeifmodified' ]
 
-import os, sys, errno
+import os, sys
 from cStringIO import StringIO
 
 from ipdl.cgen import IPDLCodeGen
-from ipdl.mgen import DependGen
 from ipdl.lower import LowerToCxx
 from ipdl.parser import Parser
 from ipdl.type import TypeCheck
@@ -73,32 +72,23 @@ def gencxx(ipdlfilename, ast, outheadersdir, outcppdir):
                           + [ resolveCpp(cpp) for cpp in cpps ]):
         tempfile = StringIO()
         CxxCodeGen(tempfile).cgen(ast)
-        writetofile(tempfile.getvalue(), filename)
+        writeifmodified(tempfile.getvalue(), filename)
 
 
 def genipdl(ast, outdir):
     return IPDLCodeGen().cgen(ast)
 
 
-def genm(ast, dir, filename):
-    tempfile = StringIO()
-    DependGen(tempfile).mgen(ast)
-    filename = dir + "/" + os.path.basename(filename) + ".depends"
-    writetofile(tempfile.getvalue(), filename)
-
-
-def writetofile(contents, file):
+def writeifmodified(contents, file):
     dir = os.path.dirname(file)
+    os.path.exists(dir) or os.makedirs(dir)
 
-    # Guard against race condition by using Try instead
-    # of |os.path.exists(dir) or os.makedirs(dir)|
-    try:
-        os.makedirs(dir)
-    except OSError, ex:
-        if ex.errno != errno.EEXIST:
-            raise ex
-        # else directory already exists. silently ignore and continue
-
-    fd = open(file, 'wb')
-    fd.write(contents)
-    fd.close()
+    oldcontents = None
+    if os.path.exists(file):
+        fd = open(file, 'rb')
+        oldcontents = fd.read()
+        fd.close()
+    if oldcontents != contents:
+        fd = open(file, 'wb')
+        fd.write(contents)
+        fd.close()
diff --git a/ipc/ipdl/ipdl/mgen.py b/ipc/ipdl/ipdl/mgen.py
deleted file mode 100644
index e68c5f07a55..00000000000
--- a/ipc/ipdl/ipdl/mgen.py
+++ /dev/null
@@ -1,54 +0,0 @@
-# ***** BEGIN LICENSE BLOCK *****
-# Version: MPL 1.1/GPL 2.0/LGPL 2.1
-#
-# The contents of this file are subject to the Mozilla Public License Version
-# 1.1 (the "License"); you may not use this file except in compliance with
-# the License. You may obtain a copy of the License at
-# http://www.mozilla.org/MPL/
-#
-# Software distributed under the License is distributed on an "AS IS" basis,
-# WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
-# for the specific language governing rights and limitations under the
-# License.
-#
-# The Original Code is mozilla.org code.
-#
-# Contributor(s):
-#   Benoit Girard <bgirard@mozilla.com>
-#
-# Alternatively, the contents of this file may be used under the terms of
-# either of the GNU General Public License Version 2 or later (the "GPL"),
-# or the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
-# in which case the provisions of the GPL or the LGPL are applicable instead
-# of those above. If you wish to allow use of your version of this file only
-# under the terms of either the GPL or the LGPL, and not to allow others to
-# use your version of this file under the terms of the MPL, indicate your
-# decision by deleting the provisions above and replace them with the notice
-# and other provisions required by the GPL or the LGPL. If you do not delete
-# the provisions above, a recipient may use your version of this file under
-# the terms of any one of the MPL, the GPL or the LGPL.
-#
-# ***** END LICENSE BLOCK *****
-
-import sys
-
-from ipdl.cgen import CodePrinter
-from ipdl.cxx.ast import TypeArray, Visitor
-
-class DependGen(CodePrinter, Visitor):
-    def __init__(self, outf=sys.stdout, indentCols=4):
-        CodePrinter.__init__(self, outf, indentCols)
-
-    def mgen(self, cxxfile):
-        cxxfile.accept(self)
-
-    def visitTranslationUnit(self, tu):
-        self.write(tu.filename)
-        self.write(": ")
-
-        for pinc in tu.protocolIncludes:
-            self.write(pinc.file)
-            self.write(" ")
-
-        self.println();
-