--- a/browser/confvars.sh
+++ b/browser/confvars.sh
@@ -62,9 +62,9 @@ fi
 MOZ_WEBGL_CONFORMANT=1
 # Enable navigator.mozPay
 MOZ_PAY=1
 # Enable activities. These are used for FxOS developers currently.
 MOZ_ACTIVITIES=1
 MOZ_JSDOWNLOADS=1
 MOZ_WEBM_ENCODER=1
 # Enable exact rooting on desktop.
-JSGC_USE_EXACT_ROOTING=1
+export JSGC_USE_EXACT_ROOTING=1

--- a/configure.in
+++ b/configure.in
@@ -3987,17 +3987,16 @@ MOZ_ANDROID_BEAM=
 MOZ_ANDROID_SYNTHAPKS=
 ACCESSIBILITY=1
 MOZ_TIME_MANAGER=
 MOZ_PAY=
 MOZ_AUDIO_CHANNEL_MANAGER=
 NSS_NO_LIBPKIX=
 MOZ_CONTENT_SANDBOX=
 MOZ_CONTENT_SANDBOX_REPORTER=1
-JSGC_USE_EXACT_ROOTING=
 
 case "$target_os" in
     mingw*)
         NS_ENABLE_TSF=1
         AC_DEFINE(NS_ENABLE_TSF)
         ;;
 esac
 
@@ -7191,71 +7190,16 @@ MOZ_ARG_ENABLE_BOOL(js-diagnostics,
 [  --enable-js-diagnostics
                           Enable JS diagnostic assertions and breakpad data],
     JS_CRASH_DIAGNOSTICS=1,
     JS_CRASH_DIAGNOSTICS= )
 if test -n "$JS_CRASH_DIAGNOSTICS"; then
     AC_DEFINE(JS_CRASH_DIAGNOSTICS)
 fi
 
-dnl ========================================================
-dnl = Use incremental GC
-dnl ========================================================
-JSGC_INCREMENTAL=1
-MOZ_ARG_DISABLE_BOOL(gcincremental,
-[  --disable-gcincremental Disable incremental GC],
-    JSGC_INCREMENTAL= )
-if test -n "$JSGC_INCREMENTAL"; then
-    AC_DEFINE(JSGC_INCREMENTAL)
-fi
-
-dnl ========================================================
-dnl = Use exact stack rooting for GC
-dnl ========================================================
-MOZ_ARG_DISABLE_BOOL(exact-rooting,
-[  --disable-exact-rooting  Enable use of conservative stack scanning for GC],
-    JSGC_USE_EXACT_ROOTING= ,
-    JSGC_USE_EXACT_ROOTING=1 )
-if test -n "$JSGC_USE_EXACT_ROOTING"; then
-    AC_DEFINE(JSGC_USE_EXACT_ROOTING)
-fi
-
-dnl ========================================================
-dnl = Use generational GC
-dnl ========================================================
-MOZ_ARG_ENABLE_BOOL(gcgenerational,
-[  --enable-gcgenerational Enable generational GC],
-    JSGC_GENERATIONAL=1,
-    JSGC_GENERATIONAL= )
-if test -n "$JSGC_GENERATIONAL"; then
-    AC_DEFINE(JSGC_GENERATIONAL)
-fi
-
-dnl ========================================================
-dnl Zealous JavaScript GC
-dnl ========================================================
-MOZ_ARG_ENABLE_BOOL(gczeal,
-[  --enable-gczeal         Enable zealous JavaScript GCing],
-    JS_GC_ZEAL=1,
-    JS_GC_ZEAL= )
-if test -n "$JS_GC_ZEAL" -o -n "$MOZ_DEBUG"; then
-    AC_DEFINE(JS_GC_ZEAL)
-fi
-
-dnl ========================================================
-dnl = Perform moving GC stack rooting analysis
-dnl ========================================================
-MOZ_ARG_ENABLE_BOOL(root-analysis,
-[  --enable-root-analysis  Enable moving GC stack root analysis],
-    JSGC_ROOT_ANALYSIS=1,
-    JSGC_ROOT_ANALYSIS= )
-if test -n "$JSGC_ROOT_ANALYSIS"; then
-    AC_DEFINE(JSGC_ROOT_ANALYSIS)
-fi
-
 MOZ_CHECK_CCACHE
 
 dnl ========================================================
 dnl = Enable static checking using gcc-dehydra
 dnl ========================================================
 
 MOZ_ARG_WITH_STRING(static-checking,
 [  --with-static-checking=path/to/gcc_dehydra.so
@@ -9247,19 +9191,16 @@ if test "$BUILD_CTYPES"; then
     ac_configure_args="$ac_configure_args --enable-ctypes"
 fi
 if test -z "$JS_SHARED_LIBRARY" ; then
     ac_configure_args="$ac_configure_args --disable-shared-js"
     if test -n "$MOZ_DISABLE_EXPORT_JS"; then
         ac_configure_args="$ac_configure_args --disable-export-js"
     fi
 fi
-if test -z "$JSGC_USE_EXACT_ROOTING" ; then
-    ac_configure_args="$ac_configure_args --disable-exact-rooting"
-fi
 if test -z "$MOZ_NATIVE_NSPR"; then
     ac_configure_args="$ac_configure_args --with-nspr-cflags='$NSPR_CFLAGS'"
     ac_configure_args="$ac_configure_args --with-nspr-libs='$NSPR_LIBS'"
 fi
 ac_configure_args="$ac_configure_args --prefix=$dist"
 if test "$MOZ_MEMORY"; then
    ac_configure_args="$ac_configure_args --enable-jemalloc"
 fi

--- a/js/src/js-config.h.in
+++ b/js/src/js-config.h.in
@@ -23,16 +23,25 @@
 
 /* Define to 1 if SpiderMonkey should include ctypes support.  */
 #undef JS_HAS_CTYPES
 
 /* Define to 1 if SpiderMonkey should support the ability to perform
    entirely too much GC.  */
 #undef JS_GC_ZEAL
 
+/* Define to 1 if SpiderMonkey should use Incremental GC. */
+#undef JSGC_INCREMENTAL
+
+/* Define to 1 if SpiderMonkey should use Generational GC. */
+#undef JSGC_GENERATIONAL
+
+/* Define to 1 if SpiderMonkey should use Compacting GC. */
+#undef JSGC_COMPACTING
+
 /* Define to 1 if the <endian.h> header is present and
    useable.  See jscpucfg.h.  */
 #undef JS_HAVE_ENDIAN_H
 
 /* Define to 1 if the <machine/endian.h> header is present and
    useable.  See jscpucfg.h.  */
 #undef JS_HAVE_MACHINE_ENDIAN_H