--- a/mozilla-tests/config.py
+++ b/mozilla-tests/config.py
@@ -2488,36 +2488,28 @@ for branch in BRANCHES.keys():
     for platform in PLATFORMS.keys():
         if platform not in BRANCHES[branch]['platforms']:
             continue
         for slave_platform in PLATFORMS[platform]['slave_platforms']:
             if slave_platform not in BRANCHES[branch]['platforms'][platform]:
                 continue
             if branch.startswith('mozilla-b2g'):
                 continue
-            bc_suite = MOCHITEST_BC_3[:]
-            dt_opt_suite = MOCHITEST_DT_2[:]
-            dt_debug_suite = MOCHITEST_DT_4[:]
-            gecko_version = BRANCHES[branch].get('gecko_version')
-            if branch in TWIGS:
-                pass
-            elif gecko_version and gecko_version != trunk_gecko_version:
-                if gecko_version > 38:
-                    # gecko_version <= 38 is a no-op for this entire if statement
-                    if slave_platform in ('ubuntu64_vm', 'ubuntu32_vm'):
-                        dt_debug_suite += MOCHITEST_DT_8[:]
-                    if slave_platform in ('ubuntu64-asan_vm',):
-                        dt_opt_suite += MOCHITEST_DT_8[:]
+            if branch in TWIGS or ('gecko_version' in BRANCHES[branch] and BRANCHES[branch]['gecko_version'] != trunk_gecko_version):
+                if slave_platform in ('ubuntu64_vm', 'ubuntu32_vm') and branch not in TWIGS:
+                    BRANCHES[branch]['platforms'][platform][slave_platform]['debug_unittest_suites'] += MOCHITEST_BC_3 + MOCHITEST_DT_8
+                else:
+                    BRANCHES[branch]['platforms'][platform][slave_platform]['debug_unittest_suites'] += MOCHITEST_BC_3 + MOCHITEST_DT_4
+                if slave_platform in ('ubuntu64-asan_vm',) and branch not in TWIGS:
+                    BRANCHES[branch]['platforms'][platform][slave_platform]['opt_unittest_suites'] += MOCHITEST_BC_3 + MOCHITEST_DT_8
+                else:
+                    BRANCHES[branch]['platforms'][platform][slave_platform]['opt_unittest_suites'] += MOCHITEST_BC_3 + MOCHITEST_DT_2
             else:
-                dt_opt_suite = MOCHITEST_DT_8[:]
-                dt_debug_suite = MOCHITEST_DT_8[:]
-                bc_suite = MOCHITEST_BC_7[:]
-            BRANCHES[branch]['platforms'][platform][slave_platform]['opt_unittest_suites'] += bc_suite + dt_opt_suite
-            BRANCHES[branch]['platforms'][platform][slave_platform]['debug_unittest_suites'] += bc_suite + dt_debug_suite
-
+                BRANCHES[branch]['platforms'][platform][slave_platform]['opt_unittest_suites'] += MOCHITEST_BC_7 + MOCHITEST_DT_8
+                BRANCHES[branch]['platforms'][platform][slave_platform]['debug_unittest_suites'] += MOCHITEST_BC_7 + MOCHITEST_DT_8
 
 # Enable mediatests on gecko >= 44 (bug 1209258)
 for name, branch in items_at_least(BRANCHES, 'gecko_version', 44):
     for platform in PLATFORMS.keys():
         if platform not in branch['platforms']:
             continue
         for slave_platform in ('ubuntu64_vm', 'ubuntu64-asan_vm', 'win7-ix', 'win8_64', 'yosemite'):
             if slave_platform in branch['platforms'][platform]: