After running an update, when launching Thunderbird it says "Your computer must be restarted to complete a previous upgrade of Thunderbird. Do you want to reboot now?". Rebooting does nothing, I'm prompted with the same message. Tried re-installing the latest version - it gives me the same error message before re-installying, and also un-installing the version I have on my PC - it also prompts me to restart to finish the earlier upgrade.