Need to shutdown program before reboot

I need to somehow have Thunderbird shutdown automatically before reboot as every time I reboot I get a warning that Thunderbird is already running.
The only option I have ATM is physically shutting it down every time I need to reboot.

How do you reboot ?

And is this Kubuntu ?

I reboot by selecting it in the menu and, yes it is Kubuntu, the one you helped me install on my laptop, 16.04.

When you say

every time I reboot I get a warning that Thunderbird is already running.

do you mean before it shuts down, or after the system starts ?

After it restarts.

I’ve done a temporary fix of removing it from the autostart list. So, now every time I reboot, it doesn’t give me the warning as it’s not trying to run a second copy of itself. For some reason, Firefox must not be completely shutting itself down