--- a/im/app/Makefile.in
+++ b/im/app/Makefile.in
@@ -111,22 +111,16 @@ RCINCLUDE = splash.rc
 EXTRA_DEPS += $(PROGRAM).manifest
 ifndef GNU_CC
 RCFLAGS += -DMOZ_INSTANTBIRD -I$(srcdir)
 else
 RCFLAGS += -DMOZ_INSTANTBIRD --include-dir $(srcdir)
 endif
 endif
 
-ifeq ($(OS_ARCH),OS2)
-RESFILE=splashos2.res
-RCFLAGS += -DMOZ_INSTANTBIRD
-RCFLAGS += -DINSTANTBIRD_ICO=\"$(DIST)/branding/instantbird.ico\"
-endif
-
 include $(topsrcdir)/config/rules.mk
 
 ifeq ($(OS_ARCH),WINNT)
 
 $(RESFILE): embedded-icons
 
 #
 # Control the default heap size.
@@ -142,22 +136,22 @@ ifndef GNU_CC
 LDFLAGS += /HEAP:0x40000
 ifeq ($(OS_TEST),x86_64)
 # set stack to 2MB on x64 build.  See bug 582910
 LDFLAGS += -STACK:2097152
 endif
 endif
 endif
 
-ifneq (,$(filter-out OS2 WINNT,$(OS_ARCH)))
+ifneq ($(OS_ARCH),WINNT)
 libs::
 	cp -p $(MOZ_APP_NAME)$(BIN_SUFFIX) $(DIST)/bin/$(MOZ_APP_NAME)-bin$(BIN_SUFFIX)
 
 GARBAGE += $(addprefix $(DIST)/bin/defaults/pref/, all.js all-instantbird.js channel-prefs.js chat-prefs.js)
-endif # ! OS 2 or WinNT
+endif # ! WinNT
 
 endif # LIBXUL_SDK
 
 ifneq (,$(filter windows gtk gtk2,$(MOZ_WIDGET_TOOLKIT)))
 ifneq (,$(filter windows,$(MOZ_WIDGET_TOOLKIT)))
 ICON_SUFFIX=.ico
 else
 ICON_SUFFIX=.png

--- a/im/content/preferences/preferences.xul
+++ b/im/content/preferences/preferences.xul
@@ -31,19 +31,16 @@
 <!ENTITY % instantbirdDTD SYSTEM "chrome://instantbird/locale/instantbird.dtd">
 %instantbirdDTD;
 #endif
 ]>
 
 #ifdef XP_WIN
 #define USE_WIN_TITLE_STYLE
 #endif
-#ifdef XP_OS2
-#define USE_WIN_TITLE_STYLE
-#endif
 
 <prefwindow type="prefwindow"
             id="BrowserPreferences"
             windowtype="Messenger:Preferences"
 #ifdef USE_WIN_TITLE_STYLE
             title="&prefWindow.titleWin;"
 #else
 #ifdef XP_UNIX

--- a/im/installer/package-manifest.in
+++ b/im/installer/package-manifest.in
@@ -629,24 +629,22 @@
 ; [Crash Reporter]
 ;
 #ifdef MOZ_CRASHREPORTER
 @BINPATH@/components/CrashService.manifest
 @BINPATH@/components/CrashService.js
 #ifdef XP_MACOSX
 @BINPATH@/crashreporter.app/
 #else
-#ifndef XP_OS2
 @BINPATH@/crashreporter@BIN_SUFFIX@
 @BINPATH@/crashreporter.ini
 #ifdef XP_UNIX
 @BINPATH@/Throbber-small.gif
 #endif
 #endif
-#endif
 #ifdef MOZ_CRASHREPORTER_INJECTOR
 @BINPATH@/breakpadinjector.dll
 #endif
 #endif
 
 ; GNOME hooks
 #ifdef MOZ_ENABLE_GNOME_COMPONENT
 @BINPATH@/components/@DLL_PREFIX@mozgnome@DLL_SUFFIX@