--- a/taskcluster/taskgraph/transforms/tests.py
+++ b/taskcluster/taskgraph/transforms/tests.py
@@ -30,16 +30,18 @@ from taskgraph.util.schema import (
 from voluptuous import (
     Any,
     Optional,
     Required,
 )
 
 import copy
 import logging
+import requests
+from collections import defaultdict
 
 WORKER_TYPE = {
     # default worker types keyed by instance-size
     'large': 'aws-provisioner-v1/gecko-t-linux-large',
     'xlarge': 'aws-provisioner-v1/gecko-t-linux-xlarge',
     'legacy': 'aws-provisioner-v1/gecko-t-linux-medium',
     'default': 'aws-provisioner-v1/gecko-t-linux-large',
     # windows / os x worker types keyed by test-platform
@@ -389,31 +391,29 @@ def set_treeherder_machine_platform(conf
             test['build-platform'], test['test-platform'])
         yield test
 
 
 @transforms.add
 def set_worker_implementation(config, tests):
     """Set the worker implementation based on the test platform."""
     for test in tests:
-        if test['test-platform'].startswith('macosx'):
-            # see if '-g' appears in try syntax
-            if config.config['args'].generic_worker:
-                test['worker-implementation'] = 'generic-worker'
-            # see if '-w' appears in try syntax
-            elif config.config['args'].taskcluster_worker:
+        test_platform = test['test-platform']
+        if test_platform.startswith('macosx'):
+            if config.config['args'].taskcluster_worker:
                 test['worker-implementation'] = 'native-engine'
             else:
-                test['worker-implementation'] = 'buildbot-bridge'
+                test['worker-implementation'] = 'generic-worker'
         elif test.get('suite', '') == 'talos':
             test['worker-implementation'] = 'buildbot-bridge'
-        elif test['test-platform'].startswith('win'):
+        elif test_platform.startswith('win'):
             test['worker-implementation'] = 'generic-worker'
         else:
             test['worker-implementation'] = 'docker-worker'
+
         yield test
 
 
 @transforms.add
 def set_tier(config, tests):
     """Set the tier based on policy for all test descriptions that do not
     specify a tier otherwise."""
     for test in tests:
@@ -663,16 +663,43 @@ def parallel_stylo_tests(config, tests):
         if test['test-platform'].startswith('linux64-stylo/'):
             # add parallel stylo tests
             test['mozharness'].setdefault('extra-options', [])\
                               .append('--parallel-stylo-traversal')
             yield test
 
 
 @transforms.add
+def allocate_to_bbb(config, tests):
+    """Make the load balancing between taskcluster and buildbot"""
+    j = get_load_balacing_settings()
+
+    tests_set = defaultdict(list)
+    for test in tests:
+        tests_set[test['test-platform']].append(test)
+
+    # Make the load balancing between taskcluster and buildbot
+    for test_platform, t in tests_set.iteritems():
+        # We sort the list to make the order of the tasks deterministic
+        t.sort(key=lambda x: (x['test-name'], x.get('this_chunk', 1)))
+        # The json file tells the percentage of tasks that run on
+        # taskcluster. The logic here is inverted, as tasks have been
+        # previously assigned to taskcluster. Therefore we assign the
+        # 1-p tasks to buildbot-bridge.
+        n = j.get(test_platform, 1.0)
+        if not (test_platform.startswith('mac')
+                and config.config['args'].taskcluster_worker):
+            for i in range(int(n * len(t)), len(t)):
+                t[i]['worker-implementation'] = 'buildbot-bridge'
+
+        for y in t:
+            yield y
+
+
+@transforms.add
 def make_job_description(config, tests):
     """Convert *test* descriptions to *job* descriptions (input to
     taskgraph.transforms.job)"""
 
     for test in tests:
         label = '{}-{}-{}'.format(config.kind, test['test-platform'], test['test-name'])
         if test['chunks'] > 1:
             label += '-{}'.format(test['this-chunk'])
@@ -762,8 +789,16 @@ def make_job_description(config, tests):
 
 def normpath(path):
     return path.replace('/', '\\')
 
 
 def get_firefox_version():
     with open('browser/config/version.txt', 'r') as f:
         return f.readline().strip()
+
+
+def get_load_balacing_settings():
+    url = "https://s3.amazonaws.com/taskcluster-graph-scheduling/tests-load.json"
+    try:
+        return requests.get(url).json()
+    except Exception:
+        return {}

--- a/taskcluster/taskgraph/try_option_syntax.py
+++ b/taskcluster/taskgraph/try_option_syntax.py
@@ -238,19 +238,16 @@ def parse_message(message):
     parser.add_argument('--no-retry', dest='no_retry', action='store_true')
     parser.add_argument('--include-nightly', dest='include_nightly', action='store_true')
 
     # While we are transitioning from BB to TC, we want to push jobs to tc-worker
     # machines but not overload machines with every try push. Therefore, we add
     # this temporary option to be able to push jobs to tc-worker.
     parser.add_argument('-w', '--taskcluster-worker',
                         dest='taskcluster_worker', action='store_true', default=False)
-    # Similarly, an extra flag for enabling os x jobs in generic-worker
-    parser.add_argument('-g', '--generic-worker',
-                        dest='generic_worker', action='store_true', default=False)
 
     # In order to run test jobs multiple times
     parser.add_argument('--rebuild', dest='trigger_tests', type=int, default=1)
     parts = parts[try_idx:] if try_idx is not None else []
     args, _ = parser.parse_known_args(parts)
     return args