how to restore my contacts that were accidently deleted

Is this a local Address Book or a network address book such as those hosted on Google, Yahoo or others? If it's local, It's probably gone for good. However, if you have a backup copy of your Thunderbird Profile it's possible to import into your current setup. If it's a network/online address book, it might be possible to connect Thunderbird to it, or to export it from their web interface and import it into Thunderbird. You need to provide more details about your current situation.