--- a/layout/tools/reftest/reftestcommandline.py
+++ b/layout/tools/reftest/reftestcommandline.py
@@ -175,25 +175,19 @@ class ReftestArgumentsParser(argparse.Ar
                           action="store",
                           type=str,
                           dest="focusFilterMode",
                           default="all",
                           help="filters tests to run by whether they require focus. "
                           "Valid values are `all', `needs-focus', or `non-needs-focus'. "
                           "Defaults to `all'.")
 
-        self.add_argument("--e10s",
-                          action="store_true",
-                          default=False,
-                          dest="e10s",
-                          help="enables content processes")
-
         self.add_argument("--disable-e10s",
                           action="store_false",
-                          default=False,
+                          default=True,
                           dest="e10s",
                           help="disables content processes")
 
         self.add_argument("--setpref",
                           action="append",
                           type=str,
                           default=[],
                           dest="extraPrefs",
@@ -749,8 +743,13 @@ class RemoteArgumentsParser(ReftestArgum
         if not options.ignoreWindowSize:
             parts = automation._devicemanager.getInfo(
                 'screen')['screen'][0].split()
             width = int(parts[0].split(':')[1])
             height = int(parts[1].split(':')[1])
             if (width < 1366 or height < 1050):
                 self.error("ERROR: Invalid screen resolution %sx%s, please adjust to 1366x1050 or higher" % (
                     width, height))
+
+        # Disable e10s by default on Android because we don't run Android
+        # e10s jobs anywhere yet.
+        options.e10s = False
+        return options

--- a/layout/tools/reftest/runreftest.py
+++ b/layout/tools/reftest/runreftest.py
@@ -647,26 +647,28 @@ class RefTest(object):
                 cmdargs.append('-marionette')
 
             profile = self.createReftestProfile(options, manifests)
             profileDir = profile.profile  # name makes more sense
 
             # browser environment
             browserEnv = self.buildBrowserEnv(options, profileDir)
 
+            self.log.info("Running with e10s: {}".format(options.e10s))
             status = self.runApp(profile,
                                  binary=options.app,
                                  cmdargs=cmdargs,
                                  # give the JS harness 30 seconds to deal with
                                  # its own timeouts
                                  env=browserEnv,
                                  timeout=options.timeout + 30.0,
                                  symbolsPath=options.symbolsPath,
                                  options=options,
                                  debuggerInfo=debuggerInfo)
+            self.log.info("Process mode: {}".format('e10s' if options.e10s else 'non-e10s'))
             mozleak.process_leak_log(self.leakLogFile,
                                      leak_thresholds=options.leakThresholds,
                                      stack_fixer=get_stack_fixer_function(options.utilityPath,
                                                                           options.symbolsPath),
             )
         finally:
             self.cleanup(profileDir)
         return status

--- a/testing/mozharness/scripts/desktop_unittest.py
+++ b/testing/mozharness/scripts/desktop_unittest.py
@@ -28,17 +28,17 @@ from mozharness.mozilla.blob_upload impo
 from mozharness.mozilla.mozbase import MozbaseMixin
 from mozharness.mozilla.testing.codecoverage import (
     CodeCoverageMixin,
     code_coverage_config_options
 )
 from mozharness.mozilla.testing.testbase import TestingMixin, testing_config_options
 
 SUITE_CATEGORIES = ['gtest', 'cppunittest', 'jittest', 'mochitest', 'reftest', 'xpcshell', 'mozbase', 'mozmill']
-SUITE_DEFAULT_E10S = ['mochitest']
+SUITE_DEFAULT_E10S = ['mochitest', 'reftest']
 
 # DesktopUnittest {{{1
 class DesktopUnittest(TestingMixin, MercurialScript, BlobUploadMixin, MozbaseMixin, CodeCoverageMixin):
     config_options = [
         [['--mochitest-suite', ], {
             "action": "extend",
             "dest": "specified_mochitest_suites",
             "type": "string",