To apply an OpenPGP alias to the account level in Thunderbird, you can follow these steps: Open Thunderbird and go to "Tools" > "Account Settings." In the Account Settings window, select the email account for which you want to apply the OpenPGP alias. Under the "OpenPGP Security" tab, check the box that says "Enable OpenPGP support for this account." Click on the "Manage OpenPGP keys" button. This will open the OpenPGP Key Manager. In the OpenPGP Key Manager, select the key associated with your email account and click on the "Properties" button. In the Key Properties window, go to the "Aliases" tab. Click on the "Add" button and enter the desired alias for your account. You can also select the checkbox that says "Use as default for this account" if you want to set the alias as the default for this account. Click "OK" to save the changes.