--- a/build/moz.configure/toolchain.configure
+++ b/build/moz.configure/toolchain.configure
@@ -135,19 +135,16 @@ set_config('MOZ_USING_SCCACHE', using_sc
 option(env='SCCACHE_VERBOSE_STATS', help='Print verbose sccache stats after build')
 
 @depends(using_sccache, 'SCCACHE_VERBOSE_STATS')
 def sccache_verbose_stats(using_sccache, verbose_stats):
     return using_sccache and bool(verbose_stats)
 
 set_config('SCCACHE_VERBOSE_STATS', sccache_verbose_stats)
 
-option(env='MOZ_HAZARD', help='Build for the GC rooting hazard analysis')
-set_config('MOZ_HAZARD', depends_if('MOZ_HAZARD')(lambda _: True))
-
 @depends('--with-compiler-wrapper', ccache)
 @imports(_from='mozbuild.shellutil', _import='split', _as='shell_split')
 def compiler_wrapper(wrapper, ccache):
     if wrapper:
         raw_wrapper = wrapper[0]
         wrapper = shell_split(raw_wrapper)
         wrapper_program = find_program(wrapper[0])
         if not wrapper_program:
@@ -167,16 +164,28 @@ add_old_configure_assignment('COMPILER_W
 
 @depends_if(compiler_wrapper)
 def using_compiler_wrapper(compiler_wrapper):
     return True
 
 set_config('MOZ_USING_COMPILER_WRAPPER', using_compiler_wrapper)
 
 
+# GC rooting and hazard analysis.
+# ==============================================================
+option(env='MOZ_HAZARD', help='Build for the GC rooting hazard analysis')
+
+@depends('MOZ_HAZARD')
+def hazard_analysis(value):
+    if value:
+        return True
+
+set_config('MOZ_HAZARD', hazard_analysis)
+
+
 # Cross-compilation related things.
 # ==============================================================
 js_option('--with-toolchain-prefix', env='TOOLCHAIN_PREFIX', nargs=1,
           help='Prefix for the target toolchain')
 
 @depends('--with-toolchain-prefix', target, cross_compiling)
 def toolchain_prefix(value, target, cross_compiling):
     if value:

--- a/toolkit/moz.configure
+++ b/toolkit/moz.configure
@@ -1085,8 +1085,40 @@ option('--enable-marionette',
        help='Enable Marionette remote protocol')
 
 @depends('--enable-marionette')
 def marionette(value):
     if value:
         return True
 
 set_config('ENABLE_MARIONETTE', marionette)
+
+# geckodriver WebDriver implementation
+# ==============================================================
+option('--enable-geckodriver', help='Enable WebDriver implementation')
+
+@depends('--enable-geckodriver',
+         'MOZ_AUTOMATION',
+         compile_environment,
+         cross_compiling,
+         hazard_analysis,
+         target)
+def geckodriver(enable, automation, compile_env, cross_compile, hazard, target):
+    """
+    geckodriver is implied on supported platforms when MOZ_AUTOMATION
+    is set, but we also provide the --enable-geckodriver option for
+    developers to use.
+
+    At the present time, we want individual developers to be able to
+    opt-in to building geckodriver locally, and for it to be enabled by
+    default on supported CI build platforms.
+    """
+    if enable:
+        return True
+
+    if enable.origin == 'default':
+        linux32 = target.kernel == 'Linux' and target.cpu == 'x86'
+        broken_platforms = cross_compile or linux32 or hazard
+
+        if automation and compile_env and not broken_platforms:
+            return True
+
+set_config('ENABLE_GECKODRIVER', geckodriver)

--- a/toolkit/toolkit.mozbuild
+++ b/toolkit/toolkit.mozbuild
@@ -149,37 +149,18 @@ if 'gtk' in CONFIG['MOZ_WIDGET_TOOLKIT']
 DIRS += ['/addon-sdk']
 
 if CONFIG['ENABLE_MARIONETTE']:
     DIRS += [
         '/testing/firefox-ui',
         '/testing/marionette',
     ]
 
-    """
-    Temporarily disable building ../testing/geckodriver
-    until https://bugzilla.mozilla.org/show_bug.cgi?id=1368035,
-    letting local developer builds opt in with --enable-geckodriver is fixed.
-
-    # Disable building of geckodriver for artifact builds and in
-    # environments where cross compiling occurs (macOS and Android),
-    # on hazard builds, and on Linux x86 (linking problems).
-    #
-    # https://bugzilla.mozilla.org/show_bug.cgi?id=1341041
-    # https://bugzilla.mozilla.org/show_bug.cgi?id=1329737
-    # https://bugzilla.mozilla.org/show_bug.cgi?id=1367519
-    # https://bugzilla.mozilla.org/show_bug.cgi?id=1367736
-    if (not CONFIG['COMPILE_ENVIRONMENT'] or
-            CONFIG['CROSS_COMPILE'] or
-            (CONFIG['OS_TARGET'] == 'Linux' and CONFIG['TARGET_CPU'] == 'i686') or
-            CONFIG['MOZ_HAZARD']):
-        pass
-    else:
-        DIRS += ['/testing/geckodriver']
-    """
+if CONFIG['ENABLE_GECKODRIVER']:
+    DIRS += ['/testing/geckodriver']
 
 DIRS += [
     '/tools/quitter',
     '/media/gmp-clearkey/0.1',
 ]
 
 if CONFIG['ENABLE_TESTS']:
     DIRS += [