How to reboot/shut down gracefully in Awesome WM?

My current configuration uses kdesu shutdown -[rh] now to reboot/shut down. The entire shutdown procedure takes about 1-2 seconds. But after every boot Firefox says it was shut down prematurely, very likely indicating that it was brutally murdered rather than laid to rest. How do I configure a "normal" WM shutdown procedure (something like kill -SIGTERM && sleep 10 && kill -SIGKILL, but preferably using **an existing tool**) in Awesome WM? Related question for GDM.