This is an old extension, the main feature is now part of thunderbird base code. You don't need this extsnion anymore.

To get the "Virtual Identity"-feeling you have to activate the "Reply from this identity when delivery headers match:" option in your account settings. Enter your domains there, like "*@example.com, *@example.de". All mails you receive now which match these domains will be answered with the right email address now (with all other settings like signature etc. of the identity where you activated this feature)