--- a/layout/tools/reftest/mach_test_package_commands.py
+++ b/layout/tools/reftest/mach_test_package_commands.py
@@ -10,16 +10,17 @@ from functools import partial
 from mach.decorators import (
     CommandProvider,
     Command,
 )
 
 
 def run_reftest(context, **kwargs):
     kwargs['app'] = kwargs['app'] or context.firefox_bin
+    kwargs['e10s'] = context.mozharness_config.get('e10s', kwargs['e10s'])
     kwargs['certPath'] = context.certs_dir
     kwargs['utilityPath'] = context.bin_dir
     kwargs['extraProfileFiles'].append(os.path.join(context.bin_dir, 'plugins'))
 
     if not kwargs['tests']:
         kwargs['tests'] = [os.path.join('layout', 'reftests', 'reftest.list')]
 
     test_root = os.path.join(context.package_root, 'reftest', 'tests')

--- a/testing/marionette/mach_test_package_commands.py
+++ b/testing/marionette/mach_test_package_commands.py
@@ -20,16 +20,17 @@ def run_marionette(context, **kwargs):
         MarionetteTestRunner,
         MarionetteHarness
     )
     from mozlog.structured import commandline
 
 
     args = argparse.Namespace(**kwargs)
     args.binary = args.binary or context.firefox_bin
+    args.e10s = context.mozharness_config.get('e10s', args.e10s)
 
     test_root = os.path.join(context.package_root, 'marionette', 'tests')
     if not args.tests:
         args.tests = [os.path.join(test_root, 'testing', 'marionette', 'harness',
                                    'marionette', 'tests', 'unit-tests.ini')]
 
     normalize = partial(context.normalize_test_path, test_root)
     args.tests = map(normalize, args.tests)

--- a/testing/mochitest/mach_test_package_commands.py
+++ b/testing/mochitest/mach_test_package_commands.py
@@ -13,16 +13,17 @@ from mach.decorators import (
     Command,
 )
 
 parser = None
 
 
 def run_mochitest(context, **kwargs):
     args = Namespace(**kwargs)
+    args.e10s = context.mozharness_config.get('e10s', args.e10s)
     args.certPath = context.certs_dir
 
     if args.test_paths:
         test_root = os.path.join(context.package_root, 'mochitest', 'tests')
         normalize = partial(context.normalize_test_path, test_root)
         args.test_paths = map(normalize, args.test_paths)
 
     return run_mochitest_desktop(context, args)

--- a/testing/xpcshell/mach_test_package_commands.py
+++ b/testing/xpcshell/mach_test_package_commands.py
@@ -17,16 +17,17 @@ from mach.decorators import (
     CommandProvider,
     Command,
 )
 
 
 def run_xpcshell(context, **kwargs):
     args = Namespace(**kwargs)
     args.appPath = args.appPath or os.path.dirname(context.firefox_bin)
+    args.e10s = context.mozharness_config.get('e10s', args.e10s)
     args.utility_path = context.bin_dir
     args.testingModulesDir = context.modules_dir
 
     if not args.xpcshell:
         args.xpcshell = os.path.join(args.appPath, 'xpcshell')
 
     if not args.pluginsPath:
         for path in context.ancestors(args.appPath, depth=2):