diff --git a/ipc/ipdl/ipdl/lower.py b/ipc/ipdl/ipdl/lower.py
index 785335ab1ad60..9a05b5734259a 100644
--- a/ipc/ipdl/ipdl/lower.py
+++ b/ipc/ipdl/ipdl/lower.py
@@ -1013,11 +1013,11 @@ def makeCxxParams(self, paramsems='in', returnsems='out',
 |params| and |returns| is the C++ semantics of those: 'in', 'out', or None."""
 
         def makeDecl(d, sems):
-            if sems is 'in':
+            if sems == 'in':
                 return Decl(d.inType(side), d.name)
-            elif sems is 'move':
+            elif sems == 'move':
                 return Decl(d.moveType(side), d.name)
-            elif sems is 'out':
+            elif sems == 'out':
                 return Decl(d.outType(side), d.name)
             else:
                 assert 0
@@ -1041,12 +1041,12 @@ def makeCallbackRejectDecl(returns):
         if paramsems is not None:
             cxxparams.extend([makeDecl(d, paramsems) for d in self.params])
 
-        if returnsems is 'promise' and self.returns:
+        if returnsems == 'promise' and self.returns:
             pass
-        elif returnsems is 'callback' and self.returns:
+        elif returnsems == 'callback' and self.returns:
             cxxparams.extend([makeCallbackResolveDecl(self.returns),
                               makeCallbackRejectDecl(self.returns)])
-        elif returnsems is 'resolver' and self.returns:
+        elif returnsems == 'resolver' and self.returns:
             cxxparams.extend([makeResolverDecl(self.returns)])
         elif returnsems is not None:
             cxxparams.extend([makeDecl(r, returnsems) for r in self.returns])
@@ -1061,31 +1061,31 @@ def makeCxxArgs(self, paramsems='in', retsems='out', retcallsems='out',
         assert not retcallsems or retsems  # retcallsems => returnsems
         cxxargs = []
 
-        if paramsems is 'move':
+        if paramsems == 'move':
             cxxargs.extend([p.mayMoveExpr() for p in self.params])
-        elif paramsems is 'in':
+        elif paramsems == 'in':
             cxxargs.extend([p.var() for p in self.params])
         else:
             assert False
 
         for ret in self.returns:
-            if retsems is 'in':
-                if retcallsems is 'in':
+            if retsems == 'in':
+                if retcallsems == 'in':
                     cxxargs.append(ret.var())
-                elif retcallsems is 'out':
+                elif retcallsems == 'out':
                     cxxargs.append(ExprAddrOf(ret.var()))
                 else:
                     assert 0
-            elif retsems is 'out':
-                if retcallsems is 'in':
+            elif retsems == 'out':
+                if retcallsems == 'in':
                     cxxargs.append(ExprDeref(ret.var()))
-                elif retcallsems is 'out':
+                elif retcallsems == 'out':
                     cxxargs.append(ret.var())
                 else:
                     assert 0
-            elif retsems is 'resolver':
+            elif retsems == 'resolver':
                 pass
-        if retsems is 'resolver':
+        if retsems == 'resolver':
             cxxargs.append(ExprMove(ExprVar('resolver')))
 
         if not implicit:
@@ -3055,7 +3055,7 @@ def visitProtocol(self, p):
                                     viz='public'))
             self.hdrfile.addthing(CppDirective('include', '"mozilla/WeakPtr.h"'))
 
-        if ptype.isToplevel() and self.side is 'parent':
+        if ptype.isToplevel() and self.side == 'parent':
             self.hdrfile.addthings([
                 _makeForwardDeclForQClass('nsIFile', []),
                 Whitespace.NL