diff --git a/src/sidebar/helpers/groups.ts b/src/sidebar/helpers/groups.ts
index 1aeaefe80b4..ecf0eb979f4 100644
--- a/src/sidebar/helpers/groups.ts
+++ b/src/sidebar/helpers/groups.ts
@@ -5,10 +5,10 @@ import type { SidebarSettings } from '../../types/config';
 import { serviceConfig } from '../config/service-config';
 
 /**
- * Should users be able to leave private groups of which they
- * are a member? Users may leave private groups unless
- * explicitly disallowed in the service configuration of the
- * `settings` object.
+ * Return true if users are allowed to leave groups.
+ *
+ * Third-party authorities currently have to opt-in to enabling this, since
+ * users may not have a way to rejoin a group after leaving.
  */
 function allowLeavingGroups(settings: SidebarSettings): boolean {
   const config = serviceConfig(settings);
@@ -42,19 +42,16 @@ export function combineGroups(
   const myGroupIds = userGroups.map(g => g.id);
   featuredGroups = featuredGroups.filter(g => !myGroupIds.includes(g.id));
 
-  // Set the isMember property indicating user membership.
+  // Set flag indicating whether user is a member of the group.
   featuredGroups.forEach(group => (group.isMember = false));
   userGroups.forEach(group => (group.isMember = true));
 
   const groups = userGroups.concat(featuredGroups);
 
-  // Set the `canLeave` property. Groups can be left if they are private unless
-  // the global `allowLeavingGroups` value is false in the config settings object.
-  groups.forEach(group => {
-    group.canLeave = !allowLeavingGroups(settings)
-      ? false
-      : group.type === 'private';
-  });
+  // Set flag indicating whether user can leave group.
+  for (const group of groups) {
+    group.canLeave = allowLeavingGroups(settings) && group.isMember;
+  }
 
   // Add isScopedToUri property indicating whether a group is within scope
   // of the given uri. If the scope check cannot be performed, isScopedToUri
diff --git a/src/sidebar/helpers/test/groups-test.js b/src/sidebar/helpers/test/groups-test.js
index 7abedf44197..dafb8c58d35 100644
--- a/src/sidebar/helpers/test/groups-test.js
+++ b/src/sidebar/helpers/test/groups-test.js
@@ -2,6 +2,7 @@ import { combineGroups, normalizeGroupIds, $imports } from '../groups';
 
 describe('sidebar/helpers/groups', () => {
   let fakeServiceConfig;
+
   describe('combineGroups', () => {
     beforeEach(() => {
       fakeServiceConfig = sinon.stub().returns(null);
@@ -22,54 +23,79 @@ describe('sidebar/helpers/groups', () => {
       assert.equal(groupA.isMember, true);
     });
 
-    it('sets `canLeave` to true if a group is private and `allowLeavingGroups` is null', () => {
-      const userGroups = [{ id: 'groupa', name: 'GroupA', type: 'private' }];
-      const featuredGroups = [{ id: 'groupb', name: 'GroupB', type: 'open' }];
-      const groups = combineGroups(
-        userGroups,
-        featuredGroups,
-        'https://foo.com/bar',
-      );
-      const groupA = groups.find(g => g.id === 'groupa');
-      const groupB = groups.find(g => g.id === 'groupb');
-      assert.equal(groupA.canLeave, true);
-      assert.equal(groupB.canLeave, false);
-    });
+    // `allowLeavingGroups` defaults to true for first party users and false
+    // for third-party users.
+    [null, { allowLeavingGroups: true }, { allowLeavingGroups: 1 }].forEach(
+      serviceConfig => {
+        it('sets `canLeave` to true if user is a member and leaving groups is enabled', () => {
+          fakeServiceConfig.returns(serviceConfig);
+          const userGroups = [
+            { id: 'groupa', name: 'GroupA', type: 'private' },
+            { id: 'groupc', name: 'GroupC', type: 'open' },
+            { id: 'groupd', name: 'GroupD', type: 'restricted' },
+          ];
+          const featuredGroups = [
+            { id: 'groupb', name: 'GroupB', type: 'open' },
+          ];
+          const groups = combineGroups(
+            userGroups,
+            featuredGroups,
+            'https://foo.com/bar',
+          );
 
-    it('sets `canLeave` to true if a group is private and `allowLeavingGroups` is not a boolean', () => {
-      fakeServiceConfig.returns({
-        allowLeavingGroups: () => {},
-      });
-      const userGroups = [{ id: 'groupa', name: 'GroupA', type: 'private' }];
-      const featuredGroups = [{ id: 'groupb', name: 'GroupB', type: 'open' }];
-      const groups = combineGroups(
-        userGroups,
-        featuredGroups,
-        'https://foo.com/bar',
-      );
-      const groupA = groups.find(g => g.id === 'groupa');
-      const groupB = groups.find(g => g.id === 'groupb');
+          const expected = [
+            {
+              id: 'groupa',
+              canLeave: true,
+            },
+            {
+              id: 'groupb',
+              canLeave: false,
+            },
+            {
+              id: 'groupc',
+              canLeave: true,
+            },
+            {
+              id: 'groupd',
+              canLeave: true,
+            },
+          ];
 
-      assert.equal(groupA.canLeave, true);
-      assert.equal(groupB.canLeave, false);
-    });
+          for (const { id, canLeave } of expected) {
+            const group = groups.find(g => g.id === id);
+            assert.strictEqual(
+              group.canLeave,
+              canLeave,
+              `incorrect canLeave for group ${id}`,
+            );
+          }
+        });
+      },
+    );
 
-    it('sets `canLeave` to false for all groups if `allowLeavingGroups` is false', () => {
-      fakeServiceConfig.returns({
-        allowLeavingGroups: false,
-      });
-      const userGroups = [{ id: 'groupa', name: 'GroupA', type: 'private' }];
-      const featuredGroups = [{ id: 'groupb', name: 'GroupB', type: 'open' }];
-      const groups = combineGroups(
-        userGroups,
-        featuredGroups,
-        'https://foo.com/bar',
-      );
-      const groupA = groups.find(g => g.id === 'groupa');
-      const groupB = groups.find(g => g.id === 'groupb');
-      assert.equal(groupA.canLeave, false);
-      assert.equal(groupB.canLeave, false);
-    });
+    [{}, { allowLeavingGroups: false }, { allowLeavingGroups: null }].forEach(
+      serviceConfig => {
+        it('sets `canLeave` to false for all groups if leaving groups is disabled', () => {
+          fakeServiceConfig.returns(serviceConfig);
+          const userGroups = [
+            { id: 'groupa', name: 'GroupA', type: 'private' },
+          ];
+          const featuredGroups = [
+            { id: 'groupb', name: 'GroupB', type: 'open' },
+          ];
+          const groups = combineGroups(
+            userGroups,
+            featuredGroups,
+            'https://foo.com/bar',
+          );
+          const groupA = groups.find(g => g.id === 'groupa');
+          const groupB = groups.find(g => g.id === 'groupb');
+          assert.equal(groupA.canLeave, false);
+          assert.equal(groupB.canLeave, false);
+        });
+      },
+    );
 
     it('combines groups from both lists uniquely', () => {
       const userGroups = [