Bug 1724089 - Remove browser.tabs.remote.autostart pref r=webdriver-reviewers,perftest-reviewers,geckoview-reviewers,jgraham,extension-reviewers,mossop,sparky,robwu,owlish,necko-reviewers,jmaher,valentin

Differential Revision: https://phabricator.services.mozilla.com/D192136

browser/app/profile/firefox.js

@@ -2184,9 +2184,6 @@ pref("privacy.fingerprintingProtection.pbmode", true);
 pref("privacy.exposeContentTitleInWindow", true);
 pref("privacy.exposeContentTitleInWindow.pbm", true);
 
-// Start the browser in e10s mode
-pref("browser.tabs.remote.autostart", true);
-
 // Run media transport in a separate process?
 pref("media.peerconnection.mtransport_process", true);
 

build/pgo/profileserver.py

@@ -124,12 +124,6 @@ if __name__ == "__main__":
                 v = v.format(**interpolation)
             prefs[k] = Preferences.cast(v)
 
-        # Enforce e10s. This isn't in one of the user.js files because those
-        # are shared with android, which doesn't want this on. We can't
-        # interpolate because the formatting code only works for strings,
-        # and this is a bool pref.
-        prefs["browser.tabs.remote.autostart"] = True
-
         profile = FirefoxProfile(
             profile=profilePath,
             preferences=prefs,

build/valgrind/mach_commands.py

@@ -99,6 +99,7 @@ def valgrind_test(command_context, suppressions):
 
         env = os.environ.copy()
         env["G_SLICE"] = "always-malloc"
+        env["MOZ_FORCE_DISABLE_E10S"] = "1"
         env["MOZ_CC_RUN_DURING_SHUTDOWN"] = "1"
         env["MOZ_CRASHREPORTER_NO_REPORT"] = "1"
         env["MOZ_DISABLE_NONLOCAL_CONNECTIONS"] = "1"

docshell/test/unit/xpcshell.toml

@@ -41,6 +41,7 @@ skip-if = ["true"]
 ["test_privacy_transition.js"]
 
 ["test_subframe_stop_after_parent_error.js"]
+disable_e10s = true
 skip-if = [
   "os == 'android'",
   "appname == 'thunderbird'", # Needs to run without E10s, can't do that.

dom/base/test/unit/xpcshell.toml

@@ -26,6 +26,7 @@ support-files = [
 ]
 
 ["test_blockParsing.js"]
+disable_e10s = true
 skip-if = [
   "debug", # We fail an assertion if we block parsing on a self-closing element
   "os == 'android'",

dom/workers/test/xpcshell/test_remoteworker_launch_new_process.js

@@ -28,12 +28,6 @@ server.registerPathHandler("/sw.js", (request, response) => {
 });
 
 add_task(async function setup_prefs() {
-  equal(
-    Services.prefs.getBoolPref("browser.tabs.remote.autostart"),
-    true,
-    "e10s is expected to be enabled"
-  );
-
   // Enable nsIServiceWorkerManager.registerForTest.
   Services.prefs.setBoolPref("dom.serviceWorkers.testing.enabled", true);
 

layout/tools/reftest/runreftest.py

@@ -471,11 +471,6 @@ class RefTest(object):
         elif manifests:
             prefs["reftest.manifests"] = json.dumps(manifests)
 
-        # Unconditionally update the e10s pref, default True
-        prefs["browser.tabs.remote.autostart"] = True
-        if not options.e10s:
-            prefs["browser.tabs.remote.autostart"] = False
-
         # default fission to True
         prefs["fission.autostart"] = True
         if options.disableFission:
@@ -529,9 +524,7 @@ class RefTest(object):
 
         self.copyExtraFilesToProfile(options, profile)
 
-        self.log.info(
-            "Running with e10s: {}".format(prefs["browser.tabs.remote.autostart"])
-        )
+        self.log.info("Running with e10s: {}".format(options.e10s))
         self.log.info("Running with fission: {}".format(prefs["fission.autostart"]))
 
         return profile
@@ -577,6 +570,9 @@ class RefTest(object):
         if options.headless:
             browserEnv["MOZ_HEADLESS"] = "1"
 
+        if not options.e10s:
+            browserEnv["MOZ_FORCE_DISABLE_E10S"] = "1"
+
         return browserEnv
 
     def cleanup(self, profileDir):

mobile/android/app/geckoview-prefs.js

@@ -142,8 +142,6 @@ pref("browser.sessionstore.max_tabs_undo", 10);
 pref("browser.sessionstore.privacy_level", 0);
 pref("browser.sessionstore.resume_from_crash", true);
 
-pref("browser.tabs.remote.autostart", true);
-
 // Bug 1809922 to enable translations
 #ifdef NIGHTLY_BUILD
   pref("browser.translations.enable", true);

modules/libpref/init/all.js

@@ -2013,9 +2013,6 @@ pref("dom.ipc.keepProcessesAlive.privilegedabout", 1);
 // Disable support for SVG
 pref("svg.disabled", false);
 
-// Disable e10s for Gecko by default. This is overridden in firefox.js.
-pref("browser.tabs.remote.autostart", false);
-
 // This pref will cause assertions when a remoteType triggers a process switch
 // to a new remoteType it should not be able to trigger.
 pref("browser.tabs.remote.enforceRemoteTypeRestrictions", false);

netwerk/test/unit/xpcshell.toml

@@ -496,10 +496,12 @@ skip-if = ["os == 'android'"] # Bug 1700483
 ["test_cookies_sync_failure.js"]
 
 ["test_cookies_thirdparty.js"]
+disable_e10s = true
 skip-if = ["appname == 'thunderbird'"]
 reason = "Thunderbird runs with fission enabled. This test requires fission.autostart=false. Bug 1749403."
 
 ["test_cookies_thirdparty_session.js"]
+disable_e10s = true
 skip-if = ["appname == 'thunderbird'"]
 reason = "Thunderbird runs with fission enabled. This test requires fission.autostart=false. Bug 1749403."
 

python/mozbuild/mozbuild/mach_commands.py

@@ -2051,11 +2051,7 @@ def _run_desktop(
         extra_env["MOZ_CRASHREPORTER"] = "1"
 
     if disable_e10s:
-        version_file = os.path.join(
-            command_context.topsrcdir, "browser", "config", "version.txt"
-        )
-        f = open(version_file, "r")
-        extra_env["MOZ_FORCE_DISABLE_E10S"] = f.read().strip()
+        extra_env["MOZ_FORCE_DISABLE_E10S"] = "1"
 
     if disable_fission:
         extra_env["MOZ_FORCE_DISABLE_FISSION"] = "1"

testing/marionette/client/marionette_driver/geckoinstance.py

@@ -439,8 +439,6 @@ class FennecInstance(GeckoInstance):
         "browser.safebrowsing.update.enabled": False,
         # Do not restore the last open set of tabs if the browser has crashed
         "browser.sessionstore.resume_from_crash": False,
-        # Disable e10s by default
-        "browser.tabs.remote.autostart": False,
     }
 
     def __init__(

testing/marionette/harness/marionette_harness/tests/unit/test_prefs.py

@@ -40,9 +40,6 @@ class TestPreferences(MarionetteTestCase):
         required_prefs = geckoinstance.DesktopInstance.desktop_prefs
 
         for key, value in six.iteritems(required_prefs):
-            if key in ["browser.tabs.remote.autostart"]:
-                return
-
             self.assertEqual(
                 self.marionette.get_pref(key),
                 value,

testing/mochitest/runtests.py

@@ -1994,6 +1994,9 @@ toolbar#nav-bar {
         if options.headless:
             browserEnv["MOZ_HEADLESS"] = "1"
 
+        if not options.e10s:
+            browserEnv["MOZ_FORCE_DISABLE_E10S"] = "1"
+
         if options.dmd:
             browserEnv["DMD"] = os.environ.get("DMD", "1")
 
@@ -2452,7 +2455,6 @@ toolbar#nav-bar {
 
         # Hardcoded prefs (TODO move these into a base profile)
         prefs = {
-            "browser.tabs.remote.autostart": options.e10s,
             # Enable tracing output for detailed failures in case of
             # failing connection attempts, and hangs (bug 1397201)
             "remote.log.level": "Trace",

testing/mochitest/tests/python/test_build_profile.py

@@ -43,10 +43,7 @@ def profile_data_dir():
 
 
 def test_common_prefs_are_all_set(build_profile, profile_data_dir):
-    # We set e10s=False here because MochitestDesktop.buildProfile overwrites
-    # the value defined in the base profile.
-    # TODO stop setting browser.tabs.remote.autostart in the base profile
-    md, result = build_profile(e10s=False)
+    md, result = build_profile()
 
     with open(os.path.join(profile_data_dir, "profiles.json"), "r") as fh:
         base_profiles = json.load(fh)["mochitest"]

testing/profiles/geckoview-junit/user.js

@@ -5,6 +5,3 @@
 // Base preferences file used by the mochitest
 /* globals user_pref */
 /* eslint quotes: 0 */
-
-// Always run in e10s
-user_pref("browser.tabs.remote.autostart", true);

testing/profiles/perf/user.js

@@ -33,7 +33,6 @@ user_pref("browser.safebrowsing.provider.mozilla.gethashURL", "http://127.0.0.1/
 user_pref("browser.safebrowsing.provider.mozilla.updateURL", "http://127.0.0.1/safebrowsing-dummy/update");
 user_pref("browser.shell.checkDefaultBrowser", false);
 user_pref("browser.startup.couldRestoreSession.count", -1);
-user_pref("browser.tabs.remote.autostart", true);
 user_pref("browser.warnOnQuit", false);
 user_pref("datareporting.healthreport.documentServerURI", "http://127.0.0.1/healthreport/");
 user_pref("devtools.chrome.enabled", false);

testing/profiles/unittest-required/user.js

@@ -49,9 +49,8 @@ user_pref("browser.shell.checkDefaultBrowser", false);
 user_pref("browser.startup.page", 0); // use about:blank, not browser.startup.homepage
 // Don't show a delay when hiding the audio indicator during tests
 user_pref("browser.tabs.delayHidingAudioPlayingIconMS", 0);
-// Don't use auto-enabled e10s
-user_pref("browser.tabs.remote.autostart", false);
-user_pref("browser.ui.layout.tablet", 0); // force tablet UI off
+// force tablet UI off
+user_pref("browser.ui.layout.tablet", 0);
 // Ensure UITour won't hit the network
 user_pref("browser.uitour.pinnedTabUrl", "http://{server}/uitour-dummy/pinnedTab");
 user_pref("browser.uitour.url", "http://{server}/uitour-dummy/tour");

testing/raptor/raptor/browsertime/android.py

@@ -190,9 +190,6 @@ class BrowsertimeAndroid(PerftestAndroid, Browsertime):
             path = os.path.join(self.profile_data_dir, "raptor-android")
             LOG.info("Merging profile: {}".format(path))
             self.profile.merge(path)
-            self.profile.set_preferences(
-                {"browser.tabs.remote.autostart": self.config["e10s"]}
-            )
 
             # There's no great way to have "after" advice in Python, so we do this
             # in super and then again here since the profile merging re-introduces

testing/raptor/raptor/perftest.py

@@ -732,9 +732,6 @@ class PerftestAndroid(Perftest):
             path = os.path.join(self.profile_data_dir, "raptor-android")
             LOG.info("Merging profile: {}".format(path))
             self.profile.merge(path)
-            self.profile.set_preferences(
-                {"browser.tabs.remote.autostart": self.config["e10s"]}
-            )
 
     def clear_app_data(self):
         LOG.info("clearing %s app data" % self.config["binary"])

testing/testsuite-targets.mk

@@ -40,10 +40,10 @@ REMOTE_REFTEST = rm -f ./$@.log && $(PYTHON3) _tests/reftest/remotereftest.py \
 
 ifeq ($(OS_ARCH),WINNT) #{
 # GPU-rendered shadow layers are unsupported here
-OOP_CONTENT = --setpref=layers.async-pan-zoom.enabled=true --setpref=browser.tabs.remote.autostart=true --setpref=layers.acceleration.disabled=true
+OOP_CONTENT = --setpref=layers.async-pan-zoom.enabled=true --setpref=layers.acceleration.disabled=true
 GPU_RENDERING =
 else
-OOP_CONTENT = --setpref=layers.async-pan-zoom.enabled=true --setpref=browser.tabs.remote.autostart=true
+OOP_CONTENT = --setpref=layers.async-pan-zoom.enabled=true
 GPU_RENDERING = --setpref=layers.acceleration.force-enabled=true
 endif #}
 

testing/web-platform/tests/tools/wptrunner/wptrunner/browsers/firefox.py

@@ -264,7 +264,7 @@ def log_gecko_crashes(logger, process, test, profile_dir, symbols_path, stackwal
         return False
 
 
-def get_environ(logger, binary, debug_info, headless, chaos_mode_flags=None):
+def get_environ(logger, binary, debug_info, headless, chaos_mode_flags=None, e10s=True):
     # Hack: test_environment expects a bin_suffix key in mozinfo that in gecko infrastructure
     # is set in the build system. Set it manually here.
     if "bin_suffix" not in mozinfo.info:
@@ -286,6 +286,8 @@ def get_environ(logger, binary, debug_info, headless, chaos_mode_flags=None):
         env["MOZ_CHAOSMODE"] = hex(chaos_mode_flags)
     if headless:
         env["MOZ_HEADLESS"] = "1"
+    if not e10s:
+        env["MOZ_FORCE_DISABLE_E10S"] = "1"
     return env
 
 
@@ -309,7 +311,7 @@ class FirefoxInstanceManager:
 
     def __init__(self, logger, binary, binary_args, profile_creator, debug_info,
                  chaos_mode_flags, headless,
-                 leak_check, stackfix_dir, symbols_path, asan):
+                 leak_check, stackfix_dir, symbols_path, asan, e10s):
         """Object that manages starting and stopping instances of Firefox."""
         self.logger = logger
         self.binary = binary
@@ -322,6 +324,7 @@ class FirefoxInstanceManager:
         self.stackfix_dir = stackfix_dir
         self.symbols_path = symbols_path
         self.asan = asan
+        self.e10s = e10s
 
         self.previous = None
         self.current = None
@@ -358,7 +361,7 @@ class FirefoxInstanceManager:
         profile.set_preferences({"marionette.port": marionette_port})
 
         env = get_environ(self.logger, self.binary, self.debug_info,
-                          self.headless, self.chaos_mode_flags)
+                          self.headless, self.chaos_mode_flags, self.e10s)
 
         args = self.binary_args[:] if self.binary_args else []
         args += [cmd_arg("marionette"), "about:blank"]
@@ -639,7 +642,7 @@ class GeckodriverOutputHandler(FirefoxOutputHandler):
 
 
 class ProfileCreator:
-    def __init__(self, logger, prefs_root, config, test_type, extra_prefs, e10s,
+    def __init__(self, logger, prefs_root, config, test_type, extra_prefs,
                  disable_fission, debug_test, browser_channel, binary, certutil_binary,
                  ca_certificate_path):
         self.logger = logger
@@ -647,7 +650,6 @@ class ProfileCreator:
         self.config = config
         self.test_type = test_type
         self.extra_prefs = extra_prefs
-        self.e10s = e10s
         self.disable_fission = disable_fission
         self.debug_test = debug_test
         self.browser_channel = browser_channel
@@ -713,8 +715,6 @@ class ProfileCreator:
             "network.proxy.type": 0,
             "places.history.enabled": False,
         })
-        if self.e10s:
-            profile.set_preferences({"browser.tabs.remote.autostart": True})
 
         profile.set_preferences({"fission.autostart": True})
         if self.disable_fission:
@@ -729,11 +729,6 @@ class ProfileCreator:
         if self.test_type == "wdspec":
             profile.set_preferences({"remote.prefs.recommended": True})
 
-        # Bug 1262954: winxp + e10s, disable hwaccel
-        if (self.e10s and platform.system() in ("Windows", "Microsoft") and
-            "5.1" in platform.version()):
-            profile.set_preferences({"layers.acceleration.disabled": True})
-
         if self.debug_test:
             profile.set_preferences({"devtools.console.stdout.content": True})
 
@@ -823,7 +818,6 @@ class FirefoxBrowser(Browser):
                                          config,
                                          test_type,
                                          extra_prefs,
-                                         e10s,
                                          disable_fission,
                                          debug_test,
                                          browser_channel,
@@ -845,7 +839,8 @@ class FirefoxBrowser(Browser):
                                                      leak_check,
                                                      stackfix_dir,
                                                      symbols_path,
-                                                     asan)
+                                                     asan,
+                                                     e10s)
 
     def settings(self, test):
         self._settings = {"check_leaks": self.leak_check and not test.leaks,
@@ -913,14 +908,13 @@ class FirefoxWdSpecBrowser(WebDriverBrowser):
         self.leak_check = leak_check
         self.leak_report_file = None
 
-        self.env = self.get_env(binary, debug_info, headless, chaos_mode_flags)
+        self.env = self.get_env(binary, debug_info, headless, chaos_mode_flags, e10s)
 
         profile_creator = ProfileCreator(logger,
                                          prefs_root,
                                          config,
                                          "wdspec",
                                          extra_prefs,
-                                         e10s,
                                          disable_fission,
                                          debug_test,
                                          browser_channel,
@@ -931,12 +925,12 @@ class FirefoxWdSpecBrowser(WebDriverBrowser):
         self.profile = profile_creator.create()
         self.marionette_port = None
 
-    def get_env(self, binary, debug_info, headless, chaos_mode_flags):
+    def get_env(self, binary, debug_info, headless, chaos_mode_flags, e10s):
         env = get_environ(self.logger,
                           binary,
                           debug_info,
                           headless,
-                          chaos_mode_flags)
+                          chaos_mode_flags, e10s)
         env["RUST_BACKTRACE"] = "1"
         return env
 

testing/web-platform/tests/tools/wptrunner/wptrunner/browsers/firefox_android.py

@@ -64,7 +64,6 @@ def browser_kwargs(logger, test_type, run_info_data, config, **kwargs):
             "timeout_multiplier": get_timeout_multiplier(test_type,
                                                          run_info_data,
                                                          **kwargs),
-            "e10s": run_info_data["e10s"],
             "disable_fission": kwargs["disable_fission"],
             # desktop only
             "leak_check": False,
@@ -93,8 +92,7 @@ def env_extras(**kwargs):
 def run_info_extras(logger, **kwargs):
     rv = fx_run_info_extras(logger, **kwargs)
     package = kwargs["package_name"]
-    rv.update({"e10s": True if package is not None and "geckoview" in package else False,
-               "headless": False})
+    rv.update({"headless": False})
 
     if kwargs["browser_version"] is None:
         rv.update(run_info_browser_version(**kwargs))
@@ -150,7 +148,7 @@ class ProfileCreator(FirefoxProfileCreator):
     def __init__(self, logger, prefs_root, config, test_type, extra_prefs,
                  disable_fission, debug_test, browser_channel, certutil_binary, ca_certificate_path):
         super().__init__(logger, prefs_root, config, test_type, extra_prefs,
-                         True, disable_fission, debug_test, browser_channel, None,
+                         disable_fission, debug_test, browser_channel, None,
                          certutil_binary, ca_certificate_path)
 
     def _set_required_prefs(self, profile):
@@ -159,7 +157,6 @@ class ProfileCreator(FirefoxProfileCreator):
             "dom.disable_open_during_load": False,
             "places.history.enabled": False,
             "dom.send_after_paint_to_content": True,
-            "browser.tabs.remote.autostart": True,
         })
 
         if self.test_type == "reftest":
@@ -191,7 +188,7 @@ class FirefoxAndroidBrowser(Browser):
     def __init__(self, logger, prefs_root, test_type, package_name="org.mozilla.geckoview.test_runner",
                  device_serial=None, extra_prefs=None, debug_info=None,
                  symbols_path=None, stackwalk_binary=None, certutil_binary=None,
-                 ca_certificate_path=None, e10s=False, stackfix_dir=None,
+                 ca_certificate_path=None, stackfix_dir=None,
                  binary_args=None, timeout_multiplier=None, leak_check=False, asan=False,
                  chaos_mode_flags=None, config=None, browser_channel="nightly",
                  install_fonts=False, tests_root=None, specialpowers_path=None, adb_binary=None,
@@ -207,7 +204,6 @@ class FirefoxAndroidBrowser(Browser):
         self.stackwalk_binary = stackwalk_binary
         self.certutil_binary = certutil_binary
         self.ca_certificate_path = ca_certificate_path
-        self.e10s = True
         self.stackfix_dir = stackfix_dir
         self.binary_args = binary_args
         self.timeout_multiplier = timeout_multiplier
@@ -351,7 +347,7 @@ class FirefoxAndroidBrowser(Browser):
 class FirefoxAndroidWdSpecBrowser(FirefoxWdSpecBrowser):
     def __init__(self, logger, prefs_root, webdriver_binary, webdriver_args,
                  extra_prefs=None, debug_info=None, symbols_path=None, stackwalk_binary=None,
-                 certutil_binary=None, ca_certificate_path=None, e10s=False,
+                 certutil_binary=None, ca_certificate_path=None,
                  disable_fission=False, stackfix_dir=None, leak_check=False,
                  asan=False, chaos_mode_flags=None, config=None,
                  browser_channel="nightly", headless=None,
@@ -361,7 +357,7 @@ class FirefoxAndroidWdSpecBrowser(FirefoxWdSpecBrowser):
         super().__init__(logger, None, prefs_root, webdriver_binary, webdriver_args,
                          extra_prefs=extra_prefs, debug_info=debug_info, symbols_path=symbols_path,
                          stackwalk_binary=stackwalk_binary, certutil_binary=certutil_binary,
-                         ca_certificate_path=ca_certificate_path, e10s=e10s,
+                         ca_certificate_path=ca_certificate_path,
                          disable_fission=disable_fission, stackfix_dir=stackfix_dir,
                          leak_check=leak_check, asan=asan,
                          chaos_mode_flags=chaos_mode_flags, config=config,
@@ -389,7 +385,7 @@ class FirefoxAndroidWdSpecBrowser(FirefoxWdSpecBrowser):
             self.logger.warning("Failed to remove forwarded or reversed ports: %s" % e)
         super().stop(force=force)
 
-    def get_env(self, binary, debug_info, headless, chaos_mode_flags):
+    def get_env(self, binary, debug_info, headless, chaos_mode_flags, e10s):
         env = get_environ(chaos_mode_flags)
         env["RUST_BACKTRACE"] = "1"
         return env

testing/xpcshell/runxpcshelltests.py

@@ -773,6 +773,9 @@ class XPCShellTestThread(Thread):
         # Check for known-fail tests
         expect_pass = self.test_object["expected"] == "pass"
 
+        if self.test_object.get("disable_e10s") == "true":
+            self.env["MOZ_FORCE_DISABLE_E10S"] = "1"
+
         # By default self.appPath will equal the gre dir. If specified in the
         # xpcshell.toml file, set a different app dir for this test.
         if self.app_dir_key and self.app_dir_key in self.test_object:

toolkit/components/extensions/test/xpcshell/head.js

@@ -56,7 +56,6 @@ Services.prefs.setBoolPref("dom.security.https_first", false);
 
 // These values may be changed in later head files and tested in check_remote
 // below.
-Services.prefs.setBoolPref("browser.tabs.remote.autostart", false);
 Services.prefs.setBoolPref("extensions.webextensions.remote", false);
 const testEnv = {
   expectRemote: false,

toolkit/components/extensions/test/xpcshell/head_e10s.js

@@ -2,7 +2,4 @@
 
 /* globals ExtensionTestUtils */
 
-// xpcshell disables e10s by default. Turn it on.
-Services.prefs.setBoolPref("browser.tabs.remote.autostart", true);
-
-ExtensionTestUtils.remoteContentScripts = true;
+// TODO bug 1863223: Remove head_e10s.js and remoteContentScripts (XPCShellContentUtils.sys.mjs)

toolkit/xre/nsAppRunner.cpp

@@ -544,7 +544,6 @@ bool gFxREmbedded = false;
 
 enum E10sStatus {
   kE10sEnabledByDefault,
-  kE10sDisabledByUser,
   kE10sForceDisabled,
 };
 
@@ -566,43 +565,18 @@ bool BrowserTabsRemoteAutostart() {
     return gBrowserTabsRemoteAutostart;
   }
 
-#if defined(MOZILLA_OFFICIAL) && MOZ_BUILD_APP_IS_BROWSER
-  bool allowSingleProcessOutsideAutomation = false;
-#else
-  bool allowSingleProcessOutsideAutomation = true;
-#endif
-
+  gBrowserTabsRemoteAutostart = true;
   E10sStatus status = kE10sEnabledByDefault;
+
   // We use "are non-local connections disabled" as a proxy for
   // "are we running some kind of automated test". It would be nicer to use
   // xpc::IsInAutomation(), but that depends on some prefs being set, which
   // they are not in (at least) gtests (where we can't) and xpcshell.
-  // Long-term, hopefully we can make tests switch to environment variables
-  // to disable e10s and then we can get rid of this.
-  if (allowSingleProcessOutsideAutomation ||
-      xpc::AreNonLocalConnectionsDisabled()) {
-    bool optInPref =
-        Preferences::GetBool("browser.tabs.remote.autostart", true);
-
-    if (optInPref) {
-      gBrowserTabsRemoteAutostart = true;
-    } else {
-      status = kE10sDisabledByUser;
-    }
-  } else {
-    gBrowserTabsRemoteAutostart = true;
-  }
-
-  // Uber override pref for emergency blocking
-  if (gBrowserTabsRemoteAutostart) {
+  // Long-term, hopefully we can make all tests e10s-friendly,
+  // then we could remove this automation-only env variable.
+  if (gBrowserTabsRemoteAutostart && xpc::AreNonLocalConnectionsDisabled()) {
     const char* forceDisable = PR_GetEnv("MOZ_FORCE_DISABLE_E10S");
-#if defined(MOZ_WIDGET_ANDROID)
-    // We need this for xpcshell on Android
-    if (forceDisable && *forceDisable) {
-#else
-    // The environment variable must match the application version to apply.
-    if (forceDisable && gAppData && !strcmp(forceDisable, gAppData->version)) {
-#endif
+    if (forceDisable && *forceDisable == '1') {
       gBrowserTabsRemoteAutostart = false;
       status = kE10sForceDisabled;
     }

widget/headless/tests/xpcshell.toml

@@ -6,6 +6,7 @@ run-if = [
 headless = true
 
 ["test_headless.js"]
+disable_e10s = true
 skip-if = ["appname == 'thunderbird'"]
 support-files = [
   "headless.html",