--- a/mozilla/thunderbird_config.py
+++ b/mozilla/thunderbird_config.py
@@ -969,16 +969,24 @@ for name, branch in items_before(BRANCHE
         branch['platforms']['macosx64']['platform_objdir'] = '%s/i386' % OBJDIR
 
 # Support cross-channel l10n in 57+ -- Bug 1397721
 for name, branch in items_at_least(BRANCHES, 'gecko_version', 57):
     if 'l10n_repo_path' not in branch:
         continue
     branch['l10n_repo_path'] = 'l10n-central'
 
+
+for name, branch in BRANCHES.items():
+    # Level 3 Branches
+    if name in ('comm-central', 'comm-beta', 'comm-esr52'):
+        for platform in branch['platforms'].values():
+            platform['env']['MOZ_SCM_LEVEL'] = '3'
+
+
 if __name__ == "__main__":
     import sys
     import pprint
     args = sys.argv[1:]
 
     if len(args) > 0:
         items = dict([(b, BRANCHES[b]) for b in args])
     else: