Have updated Thundrbird but my profile, folders, emails, address book all seem to have disappeared - how do I restore them?

I have run Thunderbird on Linux Mint for some years with no problem. Currently running Mint 18 and, with other updates in my Update Manager, have just updated Thunderbird to 68.7.0 but everything has disappeared. Hopefully it is still there on my hard drive but I need to get Thunderbird back up and running correctly as there is important information I need there.