The add-on can be made to work with tabs, but not windows:

https://support.mozilla.org/en-US/questions/1242121

If you prefer, uninstall TB 60, then install TB 52. Removing the program doesn't affect the profile folder with your data - but a profile backup is recommended, just in case.

Thanks. I use separate windows for each email, so it sounds as though I will have to uninstall the current version.

Having visited the link to the TB 52 folder, its not clear to me how I go about installing this version. This must be a question that has come up before, but a search hasn't thrown up an answer. Could you either explain or point me at a set of instructions somewhere ?

The directory for the Windows version of TB 52 is here:

http://ftp.mozilla.org/pub/thunderbird/releases/52.9.1/win32/

Choose the language, e.g. English (US) is here:

http://ftp.mozilla.org/pub/thunderbird/releases/52.9.1/win32/

Download the exe installer and run it to install TB.

Thank you - that looks clear enough. I'll do a profile backup and then uninstall TB60 and reinstall TB59.

I've now installed TB 52.9.1. Initially the Add-Ons manager said that Close On Reply was incompatible. However, I removed the Add-on and reinstalled it and all is now working fine.

Incidentally, it also says that Lightning is incompatible with 52.9.1. I don't use Lightning so do not intend to pursue this point.

Thanks for your help.