--- a/mozilla-tests/config.py
+++ b/mozilla-tests/config.py
@@ -1814,17 +1814,17 @@ BRANCHES['mozilla-release']['platforms']
 ######### mozilla-beta
 BRANCHES['mozilla-beta']['repo_path'] = "releases/mozilla-beta"
 BRANCHES['mozilla-beta']['pgo_strategy'] = 'per-checkin'
 BRANCHES['mozilla-beta']['platforms']['macosx64']['talos_slave_platforms'] = ['snowleopard', 'mountainlion']
 
 ######### mozilla-aurora
 BRANCHES['mozilla-aurora']['repo_path'] = "releases/mozilla-aurora"
 BRANCHES['mozilla-aurora']['pgo_strategy'] = 'per-checkin'
-BRANCHES['mozilla-aurora']['platforms']['macosx64']['talos_slave_platforms'] = ['snowleopard', 'mountainlion']
+BRANCHES['mozilla-aurora']['platforms']['macosx64']['talos_slave_platforms'] = ['snowleopard', 'yosemite']
 
 ######### mozilla-esr31
 BRANCHES['mozilla-esr31']['repo_path'] = "releases/mozilla-esr31"
 BRANCHES['mozilla-esr31']['pgo_strategy'] = 'per-checkin'
 BRANCHES['mozilla-esr31']['platforms']['win32']['talos_slave_platforms'] = []
 BRANCHES['mozilla-esr31']['platforms']['macosx64']['talos_slave_platforms'] = []
 BRANCHES['mozilla-esr31']['platforms']['linux']['talos_slave_platforms'] = []
 BRANCHES['mozilla-esr31']['platforms']['linux64']['talos_slave_platforms'] = []
@@ -2199,17 +2199,17 @@ for name, branch in items_at_least(BRANC
     else:
         branch['platforms']['win32']['talos_slave_platforms'] = ['xp-ix', 'win7-ix']
 
 # bug 1126493 Enable Yosemite testing on select branches only
 # keep debug tests on 10.8 until the source of the slowness is found in bug 1125998
 include_yosemite = ['try']
 for platform in PLATFORMS.keys():
     # See Bug 997946 - skip these on OS X 10.8 due to limited capacity
-    for name, branch in items_at_least(BRANCHES, 'gecko_version', 39):
+    for name, branch in items_at_least(BRANCHES, 'gecko_version', 38):
         if platform not in branch['platforms']:
             continue
         for slave_platform in branch['platforms'][platform]:
             if slave_platform not in ['mountainlion', 'yosemite']:
                 continue
             if name not in include_yosemite:
                 include_yosemite.append(name)
 delete_slave_platform(BRANCHES, PLATFORMS, {'macosx64': 'yosemite'}, branch_exclusions=include_yosemite)