Apart from the wide variety of plugins available for Mozilla Firefox and the option to configure it in the Preferences window, there is another, slightly more hidden feature to customize Firefox' behavior . To access it, enter about:config into your
How to Configure a Mail Account in Thunderbird on Linux
To add a mail account to your Thunderbird, go to Edit > Account Settings... and hit the Account Actions button beneath the menu on the left. Select Add Mail Account... and enter the name that will be shown to others,