--- a/mail/config/mozconfigs/linux32/debug
+++ b/mail/config/mozconfigs/linux32/debug
@@ -10,17 +10,16 @@ ac_add_options --enable-calendar
 . "$topsrcdir/build/mozconfig.stylo"
 
 # Needed to enable breakpad in application.ini
 export MOZILLA_OFFICIAL=1
 
 # For NSS symbols
 export MOZ_DEBUG_SYMBOLS=1
 
-ac_add_options "MOZ_ALLOW_LEGACY_EXTENSIONS=1"
 # Disable checking that add-ons are signed by the trusted root
 MOZ_ADDON_SIGNING=0
 # Disable enforcing that add-ons are signed by the trusted root
 MOZ_REQUIRE_ADDON_SIGNING=0
 
 # Package js shell
 export MOZ_PACKAGE_JSSHELL=1
 

--- a/mail/config/mozconfigs/linux32/l10n-mozconfig
+++ b/mail/config/mozconfigs/linux32/l10n-mozconfig
@@ -14,17 +14,16 @@ ac_add_options --with-l10n-base=../../l1
 ac_add_options --enable-calendar
 
 # Needed to enable breakpad in application.ini
 export MOZILLA_OFFICIAL=1
 
 # For NSS symbols
 export MOZ_DEBUG_SYMBOLS=1
 
-ac_add_options "MOZ_ALLOW_LEGACY_EXTENSIONS=1"
 # Disable checking that add-ons are signed by the trusted root
 MOZ_ADDON_SIGNING=0
 # Disable enforcing that add-ons are signed by the trusted root
 MOZ_REQUIRE_ADDON_SIGNING=0
 
 ac_add_options --disable-stdcxx-compat
 
 # Run client.py

--- a/mail/config/mozconfigs/linux32/nightly
+++ b/mail/config/mozconfigs/linux32/nightly
@@ -14,17 +14,16 @@ ac_add_options --enable-calendar
 # Needed to enable breakpad in application.ini
 export MOZILLA_OFFICIAL=1
 
 export MOZ_TELEMETRY_REPORTING=1
 
 # For NSS symbols
 export MOZ_DEBUG_SYMBOLS=1
 
-ac_add_options "MOZ_ALLOW_LEGACY_EXTENSIONS=1"
 # Disable checking that add-ons are signed by the trusted root
 MOZ_ADDON_SIGNING=0
 # Disable enforcing that add-ons are signed by the trusted root
 MOZ_REQUIRE_ADDON_SIGNING=0
 
 # Package js shell
 export MOZ_PACKAGE_JSSHELL=1
 

--- a/mail/config/mozconfigs/linux32/release
+++ b/mail/config/mozconfigs/linux32/release
@@ -13,17 +13,16 @@ ac_add_options --enable-calendar
 # Needed to enable breakpad in application.ini
 export MOZILLA_OFFICIAL=1
 
 export MOZ_TELEMETRY_REPORTING=1
 
 # For NSS symbols
 export MOZ_DEBUG_SYMBOLS=1
 
-ac_add_options "MOZ_ALLOW_LEGACY_EXTENSIONS=1"
 # Disable checking that add-ons are signed by the trusted root
 MOZ_ADDON_SIGNING=0
 # Disable enforcing that add-ons are signed by the trusted root
 MOZ_REQUIRE_ADDON_SIGNING=0
 
 # Package js shell
 export MOZ_PACKAGE_JSSHELL=1
 

--- a/mail/config/mozconfigs/linux64/l10n-mozconfig
+++ b/mail/config/mozconfigs/linux64/l10n-mozconfig
@@ -14,17 +14,16 @@ ac_add_options --with-l10n-base=../../l1
 ac_add_options --enable-calendar
 
 # Needed to enable breakpad in application.ini
 export MOZILLA_OFFICIAL=1
 
 # For NSS symbols
 export MOZ_DEBUG_SYMBOLS=1
 
-ac_add_options "MOZ_ALLOW_LEGACY_EXTENSIONS=1"
 # Disable checking that add-ons are signed by the trusted root
 MOZ_ADDON_SIGNING=0
 # Disable enforcing that add-ons are signed by the trusted root
 MOZ_REQUIRE_ADDON_SIGNING=0
 
 ac_add_options --disable-stdcxx-compat
 
 # Run client.py

--- a/mail/config/mozconfigs/linux64/nightly
+++ b/mail/config/mozconfigs/linux64/nightly
@@ -21,17 +21,16 @@ ac_add_options --enable-calendar
 # Needed to enable breakpad in application.ini
 export MOZILLA_OFFICIAL=1
 
 export MOZ_TELEMETRY_REPORTING=1
 
 # For NSS symbols
 export MOZ_DEBUG_SYMBOLS=1
 
-ac_add_options "MOZ_ALLOW_LEGACY_EXTENSIONS=1"
 # Disable checking that add-ons are signed by the trusted root
 MOZ_ADDON_SIGNING=0
 # Disable enforcing that add-ons are signed by the trusted root
 MOZ_REQUIRE_ADDON_SIGNING=0
 
 # Package js shell
 export MOZ_PACKAGE_JSSHELL=1
 

--- a/mail/config/mozconfigs/linux64/release
+++ b/mail/config/mozconfigs/linux64/release
@@ -16,17 +16,16 @@ export MOZILLA_OFFICIAL=1
 export MOZ_TELEMETRY_REPORTING=1
 
 # For NSS symbols
 export MOZ_DEBUG_SYMBOLS=1
 
 # Package js shell
 export MOZ_PACKAGE_JSSHELL=1
 
-ac_add_options "MOZ_ALLOW_LEGACY_EXTENSIONS=1"
 # Disable checking that add-ons are signed by the trusted root
 MOZ_ADDON_SIGNING=0
 # Disable enforcing that add-ons are signed by the trusted root
 MOZ_REQUIRE_ADDON_SIGNING=0
 
 # Run client.py
 mk_add_options CLIENT_PY_ARGS="$([ -f $topsrcdir/build/client.py-args ] && cat $topsrcdir/build/client.py-args)"
 mk_add_options ALWAYS_RUN_CLIENT_PY=1

--- a/mail/config/mozconfigs/macosx64/debug
+++ b/mail/config/mozconfigs/macosx64/debug
@@ -5,17 +5,16 @@ ac_add_options --enable-debug
 ac_add_options --enable-calendar
 
 # Needed to enable breakpad in application.ini
 export MOZILLA_OFFICIAL=1
 
 # For NSS symbols
 export MOZ_DEBUG_SYMBOLS=1
 
-ac_add_options "MOZ_ALLOW_LEGACY_EXTENSIONS=1"
 # Disable checking that add-ons are signed by the trusted root
 MOZ_ADDON_SIGNING=0
 # Disable enforcing that add-ons are signed by the trusted root
 MOZ_REQUIRE_ADDON_SIGNING=0
 
 # Package js shell
 export MOZ_PACKAGE_JSSHELL=1
 

--- a/mail/config/mozconfigs/macosx64/l10n-mozconfig
+++ b/mail/config/mozconfigs/macosx64/l10n-mozconfig
@@ -3,17 +3,16 @@ ac_add_options --enable-update-channel=$
 ac_add_options --disable-install-strip
 ac_add_options --enable-profiling
 ac_add_options --with-l10n-base=../../l10n
 . $topsrcdir/build/mozconfig.no-compile
 
 # Build lightning locales
 ac_add_options --enable-calendar
 
-ac_add_options "MOZ_ALLOW_LEGACY_EXTENSIONS=1"
 # Disable checking that add-ons are signed by the trusted root
 MOZ_ADDON_SIGNING=0
 # Disable enforcing that add-ons are signed by the trusted root
 MOZ_REQUIRE_ADDON_SIGNING=0
 
 # Run client.py
 mk_add_options CLIENT_PY_ARGS="$([ -f $topsrcdir/build/client.py-l10n-args ] && cat $topsrcdir/build/client.py-l10n-args)"
 mk_add_options ALWAYS_RUN_CLIENT_PY=1

--- a/mail/config/mozconfigs/macosx64/nightly
+++ b/mail/config/mozconfigs/macosx64/nightly
@@ -21,17 +21,16 @@ export MOZ_DEBUG_SYMBOLS=1
 # Needed to enable breakpad in application.ini
 export MOZILLA_OFFICIAL=1
 
 export MOZ_TELEMETRY_REPORTING=1
 
 # Package js shell
 export MOZ_PACKAGE_JSSHELL=1
 
-ac_add_options "MOZ_ALLOW_LEGACY_EXTENSIONS=1"
 # Disable checking that add-ons are signed by the trusted root
 MOZ_ADDON_SIGNING=0
 # Disable enforcing that add-ons are signed by the trusted root
 MOZ_REQUIRE_ADDON_SIGNING=0
 
 ac_add_options --with-ccache
 
 # Run client.py

--- a/mail/config/mozconfigs/macosx64/release
+++ b/mail/config/mozconfigs/macosx64/release
@@ -17,17 +17,16 @@ ac_add_options --enable-calendar
 # For NSS symbols
 export MOZ_DEBUG_SYMBOLS=1
 
 # Needed to enable breakpad in application.ini
 export MOZILLA_OFFICIAL=1
 
 export MOZ_TELEMETRY_REPORTING=1
 
-ac_add_options "MOZ_ALLOW_LEGACY_EXTENSIONS=1"
 # Disable checking that add-ons are signed by the trusted root
 MOZ_ADDON_SIGNING=0
 # Disable enforcing that add-ons are signed by the trusted root
 MOZ_REQUIRE_ADDON_SIGNING=0
 
 # Package js shell
 export MOZ_PACKAGE_JSSHELL=1
 

--- a/mail/config/mozconfigs/win32/debug
+++ b/mail/config/mozconfigs/win32/debug
@@ -15,17 +15,16 @@ ac_add_options --enable-debug
 ac_add_options --enable-calendar
 
 # Needed to enable breakpad in application.ini
 export MOZILLA_OFFICIAL=1
 
 # For NSS symbols
 export MOZ_DEBUG_SYMBOLS=1
 
-ac_add_options "MOZ_ALLOW_LEGACY_EXTENSIONS=1"
 # Disable checking that add-ons are signed by the trusted root
 MOZ_ADDON_SIGNING=0
 # Disable enforcing that add-ons are signed by the trusted root
 MOZ_REQUIRE_ADDON_SIGNING=0
 
 # Package js shell
 export MOZ_PACKAGE_JSSHELL=1
 

--- a/mail/config/mozconfigs/win32/l10n-mozconfig
+++ b/mail/config/mozconfigs/win32/l10n-mozconfig
@@ -11,17 +11,16 @@ ac_add_options --with-l10n-base=../../l1
 ac_add_options --enable-calendar
 
 # For NSS symbols
 export MOZ_DEBUG_SYMBOLS=1
 
 # Needed to enable breakpad in application.ini
 export MOZILLA_OFFICIAL=1
 
-ac_add_options "MOZ_ALLOW_LEGACY_EXTENSIONS=1"
 # Disable checking that add-ons are signed by the trusted root
 MOZ_ADDON_SIGNING=0
 # Disable enforcing that add-ons are signed by the trusted root
 MOZ_REQUIRE_ADDON_SIGNING=0
 
 # Run client.py
 mk_add_options CLIENT_PY_ARGS="$([ -f $topsrcdir/build/client.py-l10n-args ] && cat $topsrcdir/build/client.py-l10n-args)"
 mk_add_options ALWAYS_RUN_CLIENT_PY=1

--- a/mail/config/mozconfigs/win32/nightly
+++ b/mail/config/mozconfigs/win32/nightly
@@ -16,17 +16,16 @@ ac_add_options --enable-calendar
 # For NSS symbols
 export MOZ_DEBUG_SYMBOLS=1
 
 export MOZ_TELEMETRY_REPORTING=1
 
 # Needed to enable breakpad in application.ini
 export MOZILLA_OFFICIAL=1
 
-ac_add_options "MOZ_ALLOW_LEGACY_EXTENSIONS=1"
 # Disable checking that add-ons are signed by the trusted root
 MOZ_ADDON_SIGNING=0
 # Disable enforcing that add-ons are signed by the trusted root
 MOZ_REQUIRE_ADDON_SIGNING=0
 
 # Package js shell
 export MOZ_PACKAGE_JSSHELL=1
 

--- a/mail/config/mozconfigs/win32/release
+++ b/mail/config/mozconfigs/win32/release
@@ -12,17 +12,16 @@ ac_add_options --enable-calendar
 # For NSS symbols
 export MOZ_DEBUG_SYMBOLS=1
 
 export MOZ_TELEMETRY_REPORTING=1
 
 # Needed to enable breakpad in application.ini
 export MOZILLA_OFFICIAL=1
 
-ac_add_options "MOZ_ALLOW_LEGACY_EXTENSIONS=1"
 # Disable checking that add-ons are signed by the trusted root
 MOZ_ADDON_SIGNING=0
 # Disable enforcing that add-ons are signed by the trusted root
 MOZ_REQUIRE_ADDON_SIGNING=0
 
 # Package js shell
 export MOZ_PACKAGE_JSSHELL=1
 

--- a/mail/config/mozconfigs/win64/debug
+++ b/mail/config/mozconfigs/win64/debug
@@ -10,17 +10,16 @@ ac_add_options --enable-debug
 ac_add_options --enable-calendar
 
 # Needed to enable breakpad in application.ini
 export MOZILLA_OFFICIAL=1
 
 # Package js shell
 export MOZ_PACKAGE_JSSHELL=1
 
-ac_add_options "MOZ_ALLOW_LEGACY_EXTENSIONS=1"
 # Disable checking that add-ons are signed by the trusted root
 MOZ_ADDON_SIGNING=0
 # Disable enforcing that add-ons are signed by the trusted root
 MOZ_REQUIRE_ADDON_SIGNING=0
 
 . $topsrcdir/build/win64/mozconfig.vs-latest
 
 # Set up mapi includes (must be done after visual studio setup)

--- a/mail/config/mozconfigs/win64/l10n-mozconfig
+++ b/mail/config/mozconfigs/win64/l10n-mozconfig
@@ -9,17 +9,16 @@ ac_add_options --enable-update-channel=$
 . $topsrcdir/build/mozconfig.no-compile
 
 # Build lightning locales
 ac_add_options --enable-calendar
 
 # Needed to enable breakpad in application.ini
 export MOZILLA_OFFICIAL=1
 
-ac_add_options "MOZ_ALLOW_LEGACY_EXTENSIONS=1"
 # Disable checking that add-ons are signed by the trusted root
 MOZ_ADDON_SIGNING=0
 # Disable enforcing that add-ons are signed by the trusted root
 MOZ_REQUIRE_ADDON_SIGNING=0
 
 # Run client.py
 mk_add_options CLIENT_PY_ARGS="$([ -f $topsrcdir/build/client.py-args ] && cat $topsrcdir/build/client.py-args)"
 mk_add_options ALWAYS_RUN_CLIENT_PY=1

--- a/mail/config/mozconfigs/win64/nightly
+++ b/mail/config/mozconfigs/win64/nightly
@@ -11,17 +11,16 @@ ac_add_options --enable-jemalloc
 ac_add_options --enable-profiling
 ac_add_options --enable-calendar
 
 # Needed to enable breakpad in application.ini
 export MOZILLA_OFFICIAL=1
 
 export MOZ_TELEMETRY_REPORTING=1
 
-ac_add_options "MOZ_ALLOW_LEGACY_EXTENSIONS=1"
 # Disable checking that add-ons are signed by the trusted root
 MOZ_ADDON_SIGNING=0
 # Disable enforcing that add-ons are signed by the trusted root
 MOZ_REQUIRE_ADDON_SIGNING=0
 
 # Package js shell
 export MOZ_PACKAGE_JSSHELL=1
 

--- a/mail/confvars.sh
+++ b/mail/confvars.sh
@@ -6,17 +6,16 @@
 . ${_topsrcdir}/$MOZ_BUILD_APP/../comm-confvars.sh
 
 MOZ_APP_BASENAME=Thunderbird
 MOZ_APP_NAME=thunderbird
 MOZ_UPDATER=1
 MOZ_THUNDERBIRD=1
 MOZ_LDAP_XPCOM=1
 MOZ_COMPOSER=1
-MOZ_ALLOW_LEGACY_EXTENSIONS=1
 
 if test "$OS_ARCH" = "WINNT" -o \
         "$OS_ARCH" = "Linux"; then
   MOZ_BUNDLED_FONTS=1
 fi
 
 if test "$OS_ARCH" = "WINNT"; then
   MOZ_MAINTENANCE_SERVICE=1

--- a/mail/moz.configure
+++ b/mail/moz.configure
@@ -1,15 +1,16 @@
 # -*- Mode: python; c-basic-offset: 4; indent-tabs-mode: nil; tab-width: 40 -*-
 # vim: set filetype=python:
 # This Source Code Form is subject to the terms of the Mozilla Public
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 imply_option('MOZ_PLACES', True)
+imply_option('MOZ_ALLOW_LEGACY_EXTENSIONS', True)
 
 
 @depends(application)
 def is_comm_topdir(app):
     return not app[0].startswith('comm/')
 
 set_config('MOZ_IS_COMM_TOPDIR', is_comm_topdir)
 

--- a/suite/config/mozconfigs/common
+++ b/suite/config/mozconfigs/common
@@ -1,12 +1,10 @@
 # This Source Code Form is subject to the terms of the Mozilla Public
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 # This file is included by all suite mozconfigs
 
-ac_add_options "MOZ_ALLOW_LEGACY_EXTENSIONS=1"
-
 # Disable checking that add-ons are signed by the trusted root
 MOZ_ADDON_SIGNING=0
 # Disable enforcing that add-ons are signed by the trusted root
 MOZ_REQUIRE_SIGNING=0

--- a/suite/moz.configure
+++ b/suite/moz.configure
@@ -1,16 +1,17 @@
 # -*- Mode: python; c-basic-offset: 4; indent-tabs-mode: nil; tab-width: 40 -*-
 # vim: set filetype=python:
 # This Source Code Form is subject to the terms of the Mozilla Public
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 imply_option('MOZ_PLACES', True)
 imply_option('MOZ_SERVICES_SYNC', True)
+imply_option('MOZ_ALLOW_LEGACY_EXTENSIONS', True)
 
 
 @depends(application)
 def is_comm(app):
     return app[0].startswith('comm/')
 
 
 @depends(is_comm)