--- a/calendar/lightning/Makefile.in
+++ b/calendar/lightning/Makefile.in
@@ -50,17 +50,21 @@ export XPI_NAME = lightning
 export USE_EXTENSION_MANIFEST = 1
 export NO_JAR_AUTO_REG = 1
 XPI_PKGNAME = lightning
 
 STRIP_XPI = 1
 DIST_FILES = install.rdf
 PREF_JS_EXPORTS = $(srcdir)/content/lightning.js
 LIGHTNING_VERSION := $(shell cat $(srcdir)/../sunbird/config/version.txt)
+ifdef MOZILLA_1_9_1_BRANCH
+THUNDERBIRD_VERSION := $(shell cat $(topsrcdir)/mail/config/version-191.txt)
+else
 THUNDERBIRD_VERSION := $(shell cat $(topsrcdir)/mail/config/version.txt)
+endif
 SEAMONKEY_VERSION := $(shell cat $(topsrcdir)/suite/config/version.txt)
 ifdef LIGHTNING_FIREFOX
 FIREFOX_VERSION := $(shell cat $(MOZILLA_SRCDIR)/browser/config/version.txt)
 endif
 
 # include config.mk here so myconfig or app-config can set DISABLE_LIGHTNING_INSTALL
 include $(topsrcdir)/config/config.mk
 

--- a/calendar/providers/gdata/Makefile.in
+++ b/calendar/providers/gdata/Makefile.in
@@ -45,17 +45,21 @@ MODULE = gdata-provider
 
 export USE_EXTENSION_MANIFEST = 1
 export XPI_NAME = gdata-provider
 DIST_FILES = install.rdf
 XPI_PKGNAME = gdata-provider
 STRIP_XPI = 1
 
 CALENDAR_VERSION := $(shell cat $(topsrcdir)/calendar/sunbird/config/version.txt)
+ifdef MOZILLA_1_9_1_BRANCH
+THUNDERBIRD_VERSION := $(shell cat $(topsrcdir)/mail/config/version-191.txt)
+else
 THUNDERBIRD_VERSION := $(shell cat $(topsrcdir)/mail/config/version.txt)
+endif
 DEFINES += -DAB_CD=$(AB_CD) \
            -DCALENDAR_VERSION=$(CALENDAR_VERSION) \
            -DTHUNDERBIRD_VERSION=$(THUNDERBIRD_VERSION) \
            -DCOMM_BUILD=$(COMM_BUILD) \
            $(NULL)
 
 PREF_JS_EXPORTS = $(srcdir)/defaults/preferences.js
 DIRS = components locales public

--- a/calendar/timezones/Makefile.in
+++ b/calendar/timezones/Makefile.in
@@ -69,17 +69,21 @@ STRIP_XPI = 1
 PREF_JS_EXPORTS = $(srcdir)/defaults/preferences.js
 DIRS = locales
 
 ifndef DISABLE_LIGHTNING_INSTALL
 # install as a global extension in dist/bin/extensions/
 INSTALL_EXTENSION_ID = calendar-timezones@mozilla.org
 endif
 
+ifdef MOZILLA_1_9_1_BRANCH
+THUNDERBIRD_VERSION := $(shell cat $(topsrcdir)/mail/config/version-191.txt)
+else
 THUNDERBIRD_VERSION := $(shell cat $(topsrcdir)/mail/config/version.txt)
+endif
 SEAMONKEY_VERSION := $(shell cat $(topsrcdir)/suite/config/version.txt)
 CALENDAR_VERSION := $(shell cat $(topsrcdir)/calendar/sunbird/config/version.txt)
 TIMEZONES_VERSION := $(shell cat $(srcdir)/config/version.txt)
 
 DEFINES += -DAB_CD=$(AB_CD) \
            -DTHUNDERBIRD_VERSION=$(THUNDERBIRD_VERSION) \
            -DSEAMONKEY_VERSION=$(SEAMONKEY_VERSION) \
            -DCALENDAR_VERSION=$(CALENDAR_VERSION) \

--- a/configure.in
+++ b/configure.in
@@ -1594,25 +1594,25 @@ dnl Get mozilla version from central mil
 MOZILLA_VERSION=`$PERL $MOZILLA_SRCDIR/config/milestone.pl -topsrcdir $MOZILLA_SRCDIR`
 
 changequote(,)
 MOZILLA_BRANCH_VERSION=`echo ${MOZILLA_VERSION} | sed -e 's/\(^[0-9]\.[0-9]\.[0-9]\).*/\1/;'`
 changequote([,])
 
 MOZILLA_1_9_1_BRANCH=
 
+dnl Set the Gecko 1.9.1 branch version
 if test "$MOZILLA_BRANCH_VERSION" = "1.9.1"; then
     MOZILLA_1_9_1_BRANCH=1
     AC_DEFINE(MOZILLA_1_9_1_BRANCH)
 fi
 
 AC_SUBST(MOZILLA_1_9_1_BRANCH)
 
 dnl Get version of various core apps from the version files.
-THUNDERBIRD_VERSION=`cat $topsrcdir/mail/config/version.txt`
 SUNBIRD_VERSION=`cat $topsrcdir/calendar/sunbird/config/version.txt`
 SEAMONKEY_VERSION=`cat $topsrcdir/suite/config/version.txt`
 
 AC_DEFINE_UNQUOTED(MOZILLA_VERSION,"$MOZILLA_VERSION")
 AC_DEFINE_UNQUOTED(MOZILLA_VERSION_U,$MOZILLA_VERSION)
 
 dnl ========================================================
 dnl System overrides of the defaults for target

new file mode 100644
--- /dev/null
+++ b/mail/config/version-191.txt
@@ -0,0 +1,1 @@
+3.0b2pre

--- a/mail/config/version.txt
+++ b/mail/config/version.txt
@@ -1,1 +1,1 @@
-3.0b2pre
+3.1a1pre

--- a/mail/confvars.sh
+++ b/mail/confvars.sh
@@ -47,12 +47,16 @@ NECKO_PROTOCOLS_DEFAULT="about data file
 MOZ_IMG_DECODERS_DEFAULT=`echo "$MOZ_IMG_DECODERS_DEFAULT" | sed "s/ xbm//"`
 MOZ_MAIL_NEWS=1
 if [ "$COMM_BUILD" ]; then
   MOZ_LDAP_XPCOM=1
 fi
 MOZ_STATIC_MAIL_BUILD=1
 MOZ_COMPOSER=1
 MOZ_SAFE_BROWSING=1
-MOZ_APP_VERSION=`cat $topsrcdir/$MOZ_BUILD_APP/config/version.txt`
+if [ "$MOZILLA_1_9_1_BRANCH" ]; then
+  MOZ_APP_VERSION=`cat $topsrcdir/$MOZ_BUILD_APP/config/version-191.txt`
+else
+  MOZ_APP_VERSION=`cat $topsrcdir/$MOZ_BUILD_APP/config/version.txt`
+fi
 THUNDERBIRD_VERSION=$MOZ_APP_VERSION
 MOZ_EXTENSIONS_DEFAULT=" wallet"
 MOZ_NO_XPCOM_OBSOLETE=1