This is guide to setup digitally signed email with the danish NemID.
Download and install the NemID platform from: here
Installation in thunderbird
Go to account settings, select the security tab, select Security Devices.
Add NemID by selecting Load, and browse to the NemID PKCS#11, pointing at the file: C:\Program Files (x86)\Nets DanID\NemID Udvidelsesprogram\NemID_PKCS11.dll