diff --git a/relengapi/lib/auth/ldap_group_authz.py b/relengapi/lib/auth/ldap_group_authz.py
index 5102b30f..eec2473b 100644
--- a/relengapi/lib/auth/ldap_group_authz.py
+++ b/relengapi/lib/auth/ldap_group_authz.py
@@ -57,7 +57,9 @@ def get_user_groups(self, mail):
         try:
             l = ldap.initialize(self.uri)
             l.simple_bind_s(self.login_dn, self.login_password)
-            # convert mail to DN
+            groups = []
+
+            # convert mail to DN and search for groupOfNames with member=$dn
             people = l.search_s(self.user_base, ldap.SCOPE_SUBTREE,
                                 '(&(objectClass=inetOrgPerson)(mail=%s))' % (mail,), [])
             if not people or len(people) != 1:
@@ -65,9 +67,18 @@ def get_user_groups(self, mail):
             user_dn = people[0][0]
             result = l.search_s(self.group_base, ldap.SCOPE_SUBTREE,
                                 '(&(objectClass=groupOfNames)(member=%s))' % user_dn, ['cn'])
-            groups = []
             for glist in [g[1]['cn'] for g in result]:
                 groups.extend(glist)
+
+            # Mozilla uses some POSIX groups, which have a different class.
+            # The scm_level_N groups also have the unusual trait of using the mail
+            # in the memberUid attribute; other POSIX groups use the actual uid,
+            # and won't be matched by this clause
+            result = l.search_s(self.group_base, ldap.SCOPE_SUBTREE,
+                                '(&(objectClass=posixGroup)(memberUid=%s))' % mail, ['cn'])
+            for glist in [g[1]['cn'] for g in result]:
+                groups.extend(glist)
+
             return list(set(groups))
         except ldap.LDAPError:
             self.logger.exception("While connecting to the LDAP server")
diff --git a/relengapi/tests/test_lib_auth_ldap_group_authz.py b/relengapi/tests/test_lib_auth_ldap_group_authz.py
index b4166f5a..693eaf64 100644
--- a/relengapi/tests/test_lib_auth_ldap_group_authz.py
+++ b/relengapi/tests/test_lib_auth_ldap_group_authz.py
@@ -63,6 +63,11 @@ class TestGetUserGroups(unittest.TestCase):
             'cn': ['mary'],
             'mail': ['mary@org.org'],
         },
+        'cn=tom,ou=people,o=users': {
+            'objectClass': ['inetOrgPerson'],
+            'cn': ['tom'],
+            'mail': ['tom@tom.com'],
+        },
         'o=groups': {'o': 'groups'},
         'cn=authors,o=groups': {
             'objectClass': ['groupOfNames'],
@@ -79,6 +84,11 @@ class TestGetUserGroups(unittest.TestCase):
             'cn': ['c-suite'],
             'member': [],
         },
+        'cn=scm_level_17,o=groups': {
+            'objectClass': ['posixGroup'],
+            'cn': ['scm_level_17'],
+            'memberUid': ['tom@tom.com', 'mary@org.org'],
+        },
     }
 
     @classmethod
@@ -110,11 +120,16 @@ def test_get_user_groups_single(self):
         self.call(mail='jimmy@org.org', exp_groups=['authors'])
 
     def test_get_user_groups_multiple(self):
-        self.call(mail='mary@org.org', exp_groups=['authors', 'editors'])
+        # note that this includes both POSIX and normal groups
+        self.call(mail='mary@org.org',
+                  exp_groups=['authors', 'editors', 'scm_level_17'])
 
     def test_get_user_groups_nosuch(self):
         self.call(mail='steve@org.org', exp_groups=None)
 
+    def test_get_user_groups_posix(self):
+        self.call(mail='tom@tom.com', exp_groups=['scm_level_17'])
+
     @test_context.specialize(config=BAD_CONFIG)
     def test_login_fail(self, app):
         hdlr = logging.handlers.BufferingHandler(100)