--- a/config/config.mk
+++ b/config/config.mk
@@ -131,40 +131,37 @@ SLEEP ?= sleep
 TOUCH ?= touch
 
 PYTHON_PATH = $(PYTHON) $(topsrcdir)/config/pythonpath.py
 
 # determine debug-related options
 _DEBUG_ASFLAGS :=
 _DEBUG_CFLAGS :=
 _DEBUG_LDFLAGS :=
-_DEBUG_RUSTFLAGS :=
 
 ifneq (,$(MOZ_DEBUG)$(MOZ_DEBUG_SYMBOLS))
   ifeq ($(AS),$(YASM))
     ifeq ($(OS_ARCH)_$(GNU_CC),WINNT_)
       _DEBUG_ASFLAGS += -g cv8
     else
       ifneq ($(OS_ARCH),Darwin)
         _DEBUG_ASFLAGS += -g dwarf2
       endif
     endif
   else
     _DEBUG_ASFLAGS += $(MOZ_DEBUG_FLAGS)
   endif
   _DEBUG_CFLAGS += $(MOZ_DEBUG_FLAGS)
   _DEBUG_LDFLAGS += $(MOZ_DEBUG_LDFLAGS)
-  _DEBUG_RUSTFLAGS += -g
 endif
 
 ASFLAGS += $(_DEBUG_ASFLAGS)
 OS_CFLAGS += $(_DEBUG_CFLAGS)
 OS_CXXFLAGS += $(_DEBUG_CFLAGS)
 OS_LDFLAGS += $(_DEBUG_LDFLAGS)
-RUSTFLAGS += $(_DEBUG_RUSTFLAGS)
 
 # XXX: What does this? Bug 482434 filed for better explanation.
 ifeq ($(OS_ARCH)_$(GNU_CC),WINNT_)
 ifndef MOZ_DEBUG
 
 # MOZ_DEBUG_SYMBOLS generates debug symbols in separate PDB files.
 # Used for generating an optimized build with debugging symbols.
 # Used in the Windows nightlies to generate symbols for crash reporting.
@@ -284,17 +281,16 @@ else
 CFLAGS		+= $(MOZ_OPTIMIZE_FLAGS)
 CXXFLAGS	+= $(MOZ_OPTIMIZE_FLAGS)
 endif # neq (,$(MOZ_PROFILE_GENERATE)$(MOZ_PROFILE_USE))
 else
 CFLAGS		+= $(MOZ_OPTIMIZE_FLAGS)
 CXXFLAGS	+= $(MOZ_OPTIMIZE_FLAGS)
 endif # MOZ_OPTIMIZE == 1
 LDFLAGS		+= $(MOZ_OPTIMIZE_LDFLAGS)
-RUSTFLAGS	+= $(MOZ_OPTIMIZE_RUSTFLAGS)
 endif # MOZ_OPTIMIZE
 
 HOST_CFLAGS	+= $(_DEPEND_CFLAGS)
 HOST_CXXFLAGS	+= $(_DEPEND_CFLAGS)
 ifdef CROSS_COMPILE
 HOST_CFLAGS	+= $(HOST_OPTIMIZE_FLAGS)
 else
 ifdef MOZ_OPTIMIZE

--- a/old-configure.in
+++ b/old-configure.in
@@ -20,17 +20,16 @@ dnl =
 dnl ========================================================
 CFLAGS="${CFLAGS=}"
 CPPFLAGS="${CPPFLAGS=}"
 CXXFLAGS="${CXXFLAGS=}"
 LDFLAGS="${LDFLAGS=}"
 HOST_CFLAGS="${HOST_CFLAGS=}"
 HOST_CXXFLAGS="${HOST_CXXFLAGS=}"
 HOST_LDFLAGS="${HOST_LDFLAGS=}"
-RUSTFLAGS="${RUSTFLAGS=}"
 
 dnl ========================================================
 dnl = Preserve certain environment flags passed to configure
 dnl = We want sub projects to receive the same flags
 dnl = untainted by this configure script
 dnl ========================================================
 _SUBDIR_CC="$CC"
 _SUBDIR_CXX="$CXX"
@@ -4713,20 +4712,16 @@ fi
 
 dnl ========================================================
 dnl = Enable code optimization. ON by default.
 dnl ========================================================
 if test -z "$MOZ_OPTIMIZE_FLAGS"; then
     MOZ_OPTIMIZE_FLAGS="-O"
 fi
 
-if test -z "$MOZ_OPTIMIZE_RUSTFLAGS"; then
-    MOZ_OPTIMIZE_RUSTFLAGS="-O"
-fi
-
 MOZ_ARG_ENABLE_STRING(optimize,
 [  --disable-optimize      Disable compiler optimization
   --enable-optimize=[OPT] Specify compiler optimization flags [OPT=-O]],
 [ if test "$enableval" != "no"; then
     MOZ_OPTIMIZE=1
     if test -n "$enableval" -a "$enableval" != "yes"; then
         MOZ_OPTIMIZE_FLAGS=`echo "$enableval" | sed -e 's|\\\ | |g'`
         MOZ_OPTIMIZE=2
@@ -4752,17 +4747,16 @@ if test -n "$MOZ_OPTIMIZE"; then
     fi
     CFLAGS=$_SAVE_CFLAGS
 fi
 fi # COMPILE_ENVIRONMENT
 
 AC_SUBST(MOZ_OPTIMIZE)
 AC_SUBST(MOZ_FRAMEPTR_FLAGS)
 AC_SUBST(MOZ_OPTIMIZE_FLAGS)
-AC_SUBST(MOZ_OPTIMIZE_RUSTFLAGS)
 AC_SUBST(MOZ_OPTIMIZE_LDFLAGS)
 AC_SUBST_LIST(MOZ_ALLOW_HEAP_EXECUTE_FLAGS)
 AC_SUBST(MOZ_PGO)
 AC_SUBST(MOZ_PGO_OPTIMIZE_FLAGS)
 
 dnl ========================================================
 dnl = Enable NS_StackWalk.
 dnl ========================================================
@@ -6302,18 +6296,16 @@ AC_SUBST(HOST_CXXFLAGS)
 AC_SUBST(HOST_LDFLAGS)
 AC_SUBST(HOST_OPTIMIZE_FLAGS)
 AC_SUBST(HOST_AR)
 AC_SUBST(HOST_AR_FLAGS)
 AC_SUBST(HOST_LD)
 AC_SUBST(HOST_RANLIB)
 AC_SUBST(HOST_BIN_SUFFIX)
 
-AC_SUBST(RUSTFLAGS)
-
 AC_SUBST(TARGET_XPCOM_ABI)
 AC_SUBST(HAVE_TOOLCHAIN_SUPPORT_MSSSE3)
 AC_SUBST(HAVE_TOOLCHAIN_SUPPORT_MSSE4_1)
 AC_SUBST(HAVE_X86_AVX2)
 AC_SUBST(GCC_USE_GNU_LD)
 
 AC_SUBST(WRAP_LDFLAGS)
 AC_SUBST(MKSHLIB)
@@ -6649,17 +6641,16 @@ export CPP
 export CC
 export CXX
 export LD
 export ARFLAGS
 export CPPFLAGS
 export CFLAGS
 export CXXFLAGS
 export LDFLAGS
-export RUSTFLAGS
 export HOST_CC
 export HOST_CXX
 export HOST_CFLAGS
 export HOST_CPPFLAGS
 export HOST_CXXFLAGS
 export HOST_LDFLAGS
 
 if ! test -e js; then