To resolve the autofill issue in Firefox, you can try the following steps:

Open Firefox and click on the menu button (three horizontal lines) in the top right corner. Select "Options" (Windows) or "Preferences" (Mac) from the dropdown menu. In the Preferences/Options page, click on the "Privacy & Security" tab on the left side. Scroll down to the "Forms & Autofill" section. Click on the "Saved Addresses" or "Autofill" option, depending on your Firefox version. You should see a list of saved addresses or autofill data. Look for the old, expired Gmail account names and select them. Click on the "Remove" or "Delete" button to remove the unwanted entries. Repeat this process for any other old account names you want to remove. After following these steps, the old Gmail account names should no longer appear in the autofill suggestions.

Please note that the steps may vary slightly depending on your Firefox version. If you encounter any difficulties or need further assistance, feel free to ask for help in the Firefox Support Forum.

Suggestions in a login drop-down menu that have a key icon in front are login suggestions that you need to remove in the Password Manager.

• https://support.mozilla.org/en-US/kb/password-manager-remember-delete-edit-logins

Suggestions in a drop-down menu without a key symbol are autocomplete saved form data. Suggestions without a key icon are part of autocomplete saved form data that you should be able to remove by selecting this item with the cursor Down key and pressing Delete (Mac: Shift+Delete).

• https://support.mozilla.org/en-US/kb/control-whether-firefox-automatically-fills-forms

Thank you to both responders! Cor-el, yours directly solved my problem.