Yes, you can: you go on tb download page and search for 68.0.9 Download software and install it. On last step of the installation do NOT select to start tb After installed go to run (search run, select that run app) and write on that small field this: thunderbird --allow-downgrade Press enter and that's all. You will have 68 working. After that go to Option - Update - change update to manually and disable update service. After that you can search for updates manually (should suggest 68.12 - this one you can update). Please note that you will need to search on add-ons pages the versions which are working with 68.0* - those with 78* will not work