Ever since the new preferences dialog was introduced in Firefox, the UX has been quite slow. What was previously achievable through a few keystrokes now require

Ever since the new preferences dialog was introduced in Firefox, the UX has been quite slow. What was previously achievable through a few keystrokes now requires several. For your use case, you could use the Cookie Auto Delete extension and configure it appropriately. Combined with Multi Account Containers and Temporary Containers, your life will be a lot easier.