Hello there McMullen We have read your message. We try to help you.

Thunderbird has to open now Firefox appears.

Try to hold down shift while you start it. If that shows you all the missing bits then we know nothing is broken and can start steering you through possible settings changes. I'd start by running Thunderbird in Safe Mode; just hold down shift while you start it.

https://support.mozilla.org/en-US/kb/troubleshoot-mode-thunderbird#w_confirming-that-troubleshoot-mode-is-activated

After trying this give me a message back.

It could be addons turn them off and on to check if it’s them start up in Safe modus see if that change it or makes it, you also can try to uninstall the exe files and reinstall it on your pc.

Greetings Firefox volunteer.

Thank you for your help! The last few days it has been opening properly - if the problem returns I will try your advice and update you..