diff --git a/layout/tools/reftest/reftestcommandline.py b/layout/tools/reftest/reftestcommandline.py
index 83c9f105f7df..02067fcc70e2 100644
--- a/layout/tools/reftest/reftestcommandline.py
+++ b/layout/tools/reftest/reftestcommandline.py
@@ -71,7 +71,7 @@ class ReftestArgumentsParser(argparse.ArgumentParser):
                           action="store",
                           dest="timeout",
                           type=int,
-                          default=5 * 60,  # 5 minutes per bug 479518
+                          default=300,  # 5 minutes per bug 479518
                           help="reftest will timeout in specified number of seconds. "
                                "[default %(default)s].")
 
diff --git a/layout/tools/reftest/runreftest.py b/layout/tools/reftest/runreftest.py
index 7586941198a4..36c5ea10151f 100644
--- a/layout/tools/reftest/runreftest.py
+++ b/layout/tools/reftest/runreftest.py
@@ -795,10 +795,17 @@ class RefTest(object):
                 status, startAfter = 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,
+                                                 # We generally want the JS harness or marionette to handle
+                                                 # timeouts if they can.
+                                                 # The default JS harness timeout is currently 300 seconds
+                                                 # (default value of options.timeout).
+                                                 # The default Marionette socket timeout is currently 360 seconds.
+                                                 # Give the JS harness extra time to deal with its own timeouts
+                                                 # and try to usually exceed the 360 second marionette socket
+                                                 # timeout.
+                                                 # See bug 479518 and bug 1414063.
+                                                 timeout=options.timeout + 70.0,
                                                  symbolsPath=options.symbolsPath,
                                                  options=options,
                                                  debuggerInfo=debuggerInfo)
diff --git a/testing/mochitest/runtests.py b/testing/mochitest/runtests.py
index e537d041ca2f..ecc2becd4b92 100644
--- a/testing/mochitest/runtests.py
+++ b/testing/mochitest/runtests.py
@@ -2652,7 +2652,13 @@ toolbar#nav-bar {
             elif options.debugger or not options.autorun:
                 timeout = None
             else:
-                timeout = 330.0  # default JS harness timeout is 300 seconds
+                # We generally want the JS harness or marionette to handle
+                # timeouts if they can.
+                # The default JS harness timeout is currently 300 seconds.
+                # The default Marionette socket timeout is currently 360 seconds.
+                # Wait a little (10 seconds) more before timing out here.
+                # See bug 479518 and bug 1414063.
+                timeout = 370.0
 
             # Detect shutdown leaks for m-bc runs if
             # code coverage is not enabled.
diff --git a/testing/mochitest/tests/SimpleTest/TestRunner.js b/testing/mochitest/tests/SimpleTest/TestRunner.js
index 33121542626f..5c88ec44887b 100644
--- a/testing/mochitest/tests/SimpleTest/TestRunner.js
+++ b/testing/mochitest/tests/SimpleTest/TestRunner.js
@@ -88,7 +88,7 @@ TestRunner._lastAssertionCount = 0;
 TestRunner._expectedMinAsserts = 0;
 TestRunner._expectedMaxAsserts = 0;
 
-TestRunner.timeout = 5 * 60 * 1000; // 5 minutes.
+TestRunner.timeout = 300 * 1000; // 5 minutes.
 TestRunner.maxTimeouts = 4; // halt testing after too many timeouts
 TestRunner.runSlower = false;
 TestRunner.dumpOutputDirectory = "";