--- a/build/autoconf/compiler-opts.m4
+++ b/build/autoconf/compiler-opts.m4
@@ -90,40 +90,16 @@ fi
 
 dnl ========================================================
 dnl =
 dnl = Debugging Options
 dnl =
 dnl ========================================================
 AC_DEFUN([MOZ_DEBUGGING_OPTS],
 [
-dnl Debug info is ON by default.
-if test -z "$MOZ_DEBUG_FLAGS"; then
-  if test -n "$_MSC_VER"; then
-    MOZ_DEBUG_FLAGS="-Zi"
-  else
-    MOZ_DEBUG_FLAGS="-g"
-  fi
-fi
-
-AC_SUBST(MOZ_DEBUG_FLAGS)
-
-MOZ_ARG_ENABLE_STRING(debug,
-[  --enable-debug[=DBG]    Enable building with developer debug info
-                           (using compiler flags DBG)],
-[ if test "$enableval" != "no"; then
-    MOZ_DEBUG=1
-    if test -n "$enableval" -a "$enableval" != "yes"; then
-        MOZ_DEBUG_FLAGS=`echo $enableval | sed -e 's|\\\ | |g'`
-        _MOZ_DEBUG_FLAGS_SET=1
-    fi
-  else
-    MOZ_DEBUG=
-  fi ],
-  MOZ_DEBUG=)
 
 if test -z "$MOZ_DEBUG" -o -n "$MOZ_ASAN"; then
     MOZ_NO_DEBUG_RTL=1
 fi
 
 AC_SUBST(MOZ_NO_DEBUG_RTL)
 
 MOZ_DEBUG_ENABLE_DEFS="DEBUG TRACING"
@@ -151,41 +127,16 @@ if test -n "$MOZ_DEBUG"; then
 
     MOZ_DEBUG_DEFINES="$MOZ_DEBUG_ENABLE_DEFS"
 else
     MOZ_DEBUG_DEFINES="NDEBUG TRIMMED"
 fi
 
 AC_SUBST_LIST(MOZ_DEBUG_DEFINES)
 
-dnl ========================================================
-dnl = Enable generation of debug symbols
-dnl ========================================================
-MOZ_ARG_ENABLE_STRING(debug-symbols,
-[  --enable-debug-symbols[=DBG]
-                          Enable debugging symbols (using compiler flags DBG)],
-[ if test "$enableval" != "no"; then
-      MOZ_DEBUG_SYMBOLS=1
-      if test -n "$enableval" -a "$enableval" != "yes"; then
-          if test -z "$_MOZ_DEBUG_FLAGS_SET"; then
-              MOZ_DEBUG_FLAGS=`echo $enableval | sed -e 's|\\\ | |g'`
-          else
-              AC_MSG_ERROR([--enable-debug-symbols flags cannot be used with --enable-debug flags])
-          fi
-      fi
-  else
-      MOZ_DEBUG_SYMBOLS=
-  fi ],
-  MOZ_DEBUG_SYMBOLS=1)
-
-if test -n "$MOZ_DEBUG" -o -n "$MOZ_DEBUG_SYMBOLS"; then
-    AC_DEFINE(MOZ_DEBUG_SYMBOLS)
-    export MOZ_DEBUG_SYMBOLS
-fi
-
 ])
 
 dnl A high level macro for selecting compiler options.
 AC_DEFUN([MOZ_COMPILER_OPTS],
 [
   MOZ_DEBUGGING_OPTS
   MOZ_RTTI
 if test "$CLANG_CXX"; then

--- a/build/moz.configure/old.configure
+++ b/build/moz.configure/old.configure
@@ -167,19 +167,17 @@ def old_configure_options(*options):
     '--enable-clang-plugin',
     '--enable-content-sandbox',
     '--enable-cookies',
     '--enable-cpp-rtti',
     '--enable-crashreporter',
     '--enable-ctypes',
     '--enable-dbm',
     '--enable-dbus',
-    '--enable-debug',
     '--enable-debug-js-modules',
-    '--enable-debug-symbols',
     '--enable-directshow',
     '--enable-dtrace',
     '--enable-dump-painting',
     '--enable-elf-hack',
     '--enable-extensions',
     '--enable-faststripe',
     '--enable-feeds',
     '--enable-gamepad',

--- a/build/moz.configure/toolchain.configure
+++ b/build/moz.configure/toolchain.configure
@@ -599,8 +599,52 @@ def compiler(language, host_or_target, c
 
 
 c_compiler = compiler('C', target)
 cxx_compiler = compiler('C++', target, c_compiler=c_compiler)
 host_c_compiler = compiler('C', host, other_compiler=c_compiler)
 host_cxx_compiler = compiler('C++', host, c_compiler=host_c_compiler,
                              other_compiler=cxx_compiler,
                              other_c_compiler=c_compiler)
+
+@depends(c_compiler)
+def default_debug_flags(compiler_info):
+    # Debug info is ON by default.
+    if compiler_info.type == 'msvc':
+        return '-Zi'
+    return '-g'
+
+option(env='MOZ_DEBUG_FLAGS',
+       nargs=1,
+       help='Debug compiler flags')
+
+js_option('--enable-debug-symbols',
+          nargs='?',
+          default=True,
+          help='Enable debug symbols using the given compiler flags')
+
+@depends('--enable-debug-symbols', '--enable-debug')
+def debug_symbols(debug_symbols, debug):
+    if debug_symbols or debug:
+        return True
+
+set_config('MOZ_DEBUG_SYMBOLS', debug_symbols)
+
+@depends('MOZ_DEBUG_FLAGS', '--enable-debug', '--enable-debug-symbols',
+         default_debug_flags)
+def debug_flags(env_debug_flags, enable_debug_flags, debug_symbols_flags,
+                default_debug_flags):
+    if len(enable_debug_flags) and len(debug_symbols_flags):
+        die('--enable-debug-symbols flags cannot be used with --enable-debug flags')
+    # If MOZ_DEBUG_FLAGS is set, and --enable-debug is set to a value,
+    # --enable-debug takes precedence.
+    if len(enable_debug_flags):
+        return enable_debug_flags[0]
+    # If MOZ_DEBUG_FLAGS is set, and --enable-debug-symbols is set to a value,
+    # --enable-debug-symbols takes precedence.
+    if len(debug_symbols_flags):
+        return debug_symbols_flags[0]
+    if env_debug_flags:
+        return env_debug_flags[0]
+    return default_debug_flags
+
+set_config('MOZ_DEBUG_FLAGS', debug_flags)
+add_old_configure_assignment('MOZ_DEBUG_FLAGS', debug_flags)

--- a/js/src/old-configure.in
+++ b/js/src/old-configure.in
@@ -2446,17 +2446,16 @@ AC_SUBST(AS_DASH_C_FLAG)
 AC_SUBST(LD)
 AC_SUBST(RC)
 AC_SUBST(RCFLAGS)
 AC_SUBST(WINDRES)
 AC_SUBST(IMPLIB)
 AC_SUBST(FILTER)
 AC_SUBST(BIN_FLAGS)
 AC_SUBST(MOZ_DEBUG)
-AC_SUBST(MOZ_DEBUG_SYMBOLS)
 AC_SUBST(MOZ_DEBUG_LDFLAGS)
 AC_SUBST(WARNINGS_AS_ERRORS)
 AC_SUBST(LIBICONV)
 
 AC_SUBST(ENABLE_STRIP)
 AC_SUBST(PKG_SKIP_STRIP)
 AC_SUBST(INCREMENTAL_LINKER)
 

--- a/moz.configure
+++ b/moz.configure
@@ -80,16 +80,24 @@ def linux_gtest_defines(target, enable_t
 
 set_define('GTEST_OS_LINUX_ANDROID',
            delayed_getattr(linux_gtest_defines, 'os_linux_android'))
 set_define('GTEST_USE_OWN_TR1_TUPLE',
            delayed_getattr(linux_gtest_defines, 'use_own_tr1_tuple'))
 set_define('GTEST_HAS_CLONE',
            delayed_getattr(linux_gtest_defines, 'has_clone'))
 
+js_option('--enable-debug',
+          nargs='?',
+          help='Enable building with developer debug info '
+               '(using the given compiler flags).')
+
+add_old_configure_assignment('MOZ_DEBUG',
+                             depends_if('--enable-debug')(lambda _: True))
+
 @depends('--disable-compile-environment', '--help')
 def toolchain_include(compile_env, help):
     if compile_env:
         return 'build/moz.configure/toolchain.configure'
 
 include(toolchain_include)
 
 @depends('--disable-compile-environment', '--help')

--- a/old-configure.in
+++ b/old-configure.in
@@ -6479,17 +6479,16 @@ AC_SUBST(RC)
 AC_SUBST(RCFLAGS)
 AC_SUBST(WINDRES)
 AC_SUBST(IMPLIB)
 AC_SUBST(FILTER)
 AC_SUBST(BIN_FLAGS)
 AC_SUBST(MOZ_AUTH_EXTENSION)
 AC_SUBST(MOZ_PREF_EXTENSIONS)
 AC_SUBST(MOZ_DEBUG)
-AC_SUBST(MOZ_DEBUG_SYMBOLS)
 AC_SUBST(MOZ_DEBUG_LDFLAGS)
 AC_SUBST(WARNINGS_AS_ERRORS)
 AC_SUBST_SET(MOZ_EXTENSIONS)
 AC_SUBST(LIBICONV)
 AC_SUBST(MOZ_TOOLKIT_SEARCH)
 AC_SUBST(MOZ_FEEDS)
 AC_SUBST(NS_PRINTING)
 AC_SUBST(MOZ_HELP_VIEWER)