--- a/extensions/permissions/nsPermissionManager.cpp
+++ b/extensions/permissions/nsPermissionManager.cpp
@@ -1693,16 +1693,28 @@ nsresult nsPermissionManager::AddInterna
     nsIPrincipal* aPrincipal, const nsACString& aType, uint32_t aPermission,
     int64_t aID, uint32_t aExpireType, int64_t aExpireTime,
     int64_t aModificationTime, NotifyOperationType aNotifyOperation,
     DBOperationType aDBOperation, const bool aIgnoreSessionPermissions) {
   nsAutoCString origin;
   nsresult rv = GetOriginFromPrincipal(aPrincipal, origin);
   NS_ENSURE_SUCCESS(rv, rv);
 
+  // For private browsing only store permissions for the session
+  if (aExpireType != EXPIRE_SESSION) {
+    uint32_t privateBrowsingId =
+        nsScriptSecurityManager::DEFAULT_PRIVATE_BROWSING_ID;
+    nsresult rv = aPrincipal->GetPrivateBrowsingId(&privateBrowsingId);
+    if (NS_SUCCEEDED(rv) &&
+        privateBrowsingId !=
+            nsScriptSecurityManager::DEFAULT_PRIVATE_BROWSING_ID) {
+      aExpireType = EXPIRE_SESSION;
+    }
+  }
+
   if (!IsChildProcess()) {
     IPC::Permission permission(origin, aType, aPermission, aExpireType,
                                aExpireTime);
 
     nsAutoCString permissionKey;
     GetKeyForPermission(aPrincipal, aType, permissionKey);
 
     nsTArray<ContentParent*> cplist;

--- a/extensions/permissions/test/unit/test_permmanager_expiration.js
+++ b/extensions/permissions/test/unit/test_permmanager_expiration.js
@@ -131,10 +131,29 @@ function* do_run_test() {
     null,
     pm.getPermissionObject(principal, "test/expiration-perm-exp2", false)
   );
   Assert.equal(
     null,
     pm.getPermissionObject(principal, "test/expiration-session-exp2", false)
   );
 
+  // Add a persistent permission for private browsing
+  let principalPB = Services.scriptSecurityManager.createContentPrincipal(
+    permURI,
+    { privateBrowsingId: 1 }
+  );
+  pm.addFromPrincipal(
+    principalPB,
+    "test/expiration-session-pb",
+    pm.ALLOW_ACTION
+  );
+
+  // The permission should be set to session expiry
+  let perm = pm.getPermissionObject(
+    principalPB,
+    "test/expiration-session-pb",
+    true
+  );
+  Assert.equal(perm.expireType, pm.EXPIRE_SESSION);
+
   do_finish_generator_test(test_generator);
 }