diff --git a/build/moz.configure/init.configure b/build/moz.configure/init.configure
index 8299062f2f6a..6b9df42b2c39 100644
--- a/build/moz.configure/init.configure
+++ b/build/moz.configure/init.configure
@@ -563,6 +563,39 @@ def build_project(include_project_configure, build_env, help):
     return ret
 
 
+# set RELEASE_BUILD and NIGHTLY_BUILD variables depending on the cycle we're in
+# The logic works like this:
+# - if we have "a1" in GRE_MILESTONE, we're building Nightly (define NIGHTLY_BUILD)
+# - otherwise, if we have "a" in GRE_MILESTONE, we're building Nightly or Aurora
+# - otherwise, we're building Release/Beta (define RELEASE_BUILD)
+@depends(check_build_environment)
+@advanced
+def milestone(build_env):
+    milestone_path = os.path.join(build_env['TOPSRCDIR'],
+                                  'config',
+                                  'milestone.txt')
+    with open(milestone_path, 'r') as fh:
+        milestone = fh.read().splitlines()[-1]
+
+    set_config('GRE_MILESTONE', milestone)
+
+    is_nightly = is_release = False
+
+    if 'a1' in milestone:
+        set_config('NIGHTLY_BUILD', '1')
+        set_define('NIGHTLY_BUILD', '1')
+        add_old_configure_assignment('NIGHTLY_BUILD', '1')
+        is_nightly = True
+    elif 'a' not in milestone:
+        set_config('RELEASE_BUILD', '1')
+        set_define('RELEASE_BUILD', '1')
+        add_old_configure_assignment('RELEASE_BUILD', '1')
+        is_release = True
+
+    return namespace(version=milestone,
+                     is_nightly=is_nightly,
+                     is_release=is_release)
+
 # This is temporary until js/src/configure and configure are merged.
 # Use instead of option() in js/moz.configure
 @template
diff --git a/js/src/old-configure.in b/js/src/old-configure.in
index 7693a4537d5a..7d4bba847e6d 100644
--- a/js/src/old-configure.in
+++ b/js/src/old-configure.in
@@ -1897,32 +1897,6 @@ fi
 AC_DEFINE_UNQUOTED(MOZ_UPDATE_CHANNEL, $MOZ_UPDATE_CHANNEL)
 AC_SUBST(MOZ_UPDATE_CHANNEL)
 
-
-dnl set GRE_MILESTONE
-dnl ========================================================
-GRE_MILESTONE=`tail -n 1 "$_topsrcdir"/config/milestone.txt 2>/dev/null || tail -1 "$_topsrcdir"/config/milestone.txt`
-AC_SUBST(GRE_MILESTONE)
-
-dnl set RELEASE_BUILD and NIGHTLY_BUILD variables depending on the cycle we're in
-dnl The logic works like this:
-dnl - if we have "a1" in GRE_MILESTONE, we're building Nightly (define NIGHTLY_BUILD)
-dnl - otherwise, if we have "a" in GRE_MILESTONE, we're building Nightly or Aurora
-dnl - otherwise, we're building Release/Beta (define RELEASE_BUILD)
-case "$GRE_MILESTONE" in
-  *a1*)
-      NIGHTLY_BUILD=1
-      AC_DEFINE(NIGHTLY_BUILD)
-      ;;
-  *a*)
-      ;;
-  *)
-      RELEASE_BUILD=1
-      AC_DEFINE(RELEASE_BUILD)
-      ;;
-esac
-AC_SUBST(NIGHTLY_BUILD)
-AC_SUBST(RELEASE_BUILD)
-
 dnl ========================================================
 dnl =
 dnl = Check for external package dependencies
diff --git a/moz.configure b/moz.configure
index 82fc28db874e..5a34e3f8fc68 100644
--- a/moz.configure
+++ b/moz.configure
@@ -15,6 +15,15 @@ include('build/moz.configure/checks.configure')
 # - Spidermonkey-specific options and rules should go in js/moz.configure.
 # - etc.
 
+# Multiprocess Firefox Testing UI - Nightly and Aurora
+# To be removed in Bug 1003313
+@depends(milestone)
+def e10s_testing_only(milestone):
+    if not milestone.is_release:
+        set_config('E10S_TESTING_ONLY', '1')
+        set_define('E10S_TESTING_ONLY', '1')
+
+
 option('--enable-artifact-builds', env='MOZ_ARTIFACT_BUILDS',
        help='Download and use prebuilt binary artifacts.')
 
diff --git a/old-configure.in b/old-configure.in
index 9089446c4b86..3158bbd0d219 100644
--- a/old-configure.in
+++ b/old-configure.in
@@ -2549,42 +2549,6 @@ esac
 
 MOZ_CONFIG_NSPR()
 
-dnl set GRE_MILESTONE
-dnl ========================================================
-GRE_MILESTONE=`tail -n 1 "$_topsrcdir"/config/milestone.txt 2>/dev/null || tail -1 "$_topsrcdir"/config/milestone.txt`
-AC_SUBST(GRE_MILESTONE)
-
-# set RELEASE_BUILD and NIGHTLY_BUILD variables depending on the cycle we're in
-# The logic works like this:
-# - if we have "a1" in GRE_MILESTONE, we're building Nightly (define NIGHTLY_BUILD)
-# - otherwise, if we have "a" in GRE_MILESTONE, we're building Nightly or Aurora
-# - otherwise, we're building Release/Beta (define RELEASE_BUILD)
-case "$GRE_MILESTONE" in
-  *a1*)
-      NIGHTLY_BUILD=1
-      AC_DEFINE(NIGHTLY_BUILD)
-      ;;
-  *a*)
-      ;;
-  *)
-      RELEASE_BUILD=1
-      AC_DEFINE(RELEASE_BUILD)
-      ;;
-esac
-AC_SUBST(NIGHTLY_BUILD)
-AC_SUBST(RELEASE_BUILD)
-
-dnl ========================================================
-dnl Multiprocess Firefox Testing UI - Nightly and Aurora
-dnl To be removed in Bug 1003313
-dnl ========================================================
-if test -z "$RELEASE_BUILD"; then
-    E10S_TESTING_ONLY=1
-    AC_DEFINE(E10S_TESTING_ONLY)
-fi
-
-AC_SUBST(E10S_TESTING_ONLY)
-
 dnl ========================================================
 dnl system libevent Support
 dnl ========================================================