Yes, of course. Both Firefox and Thunderbird are compatible with Windows 10. Please see How to install Firefox on Windows and Installing Thunderbird on Windows articles.

Do you want to synchronize or migrate any data from your old computer?

Thanks Michael for that and yes will be wanting to migrate the data over from our old computer. It will save a lot of work putting the info in again Sue

You're welcome.

What data do you want to migrate? For Firefox, I would advise you to synchronize both computers using Firefox Sync.

For Thunderbird moving its whole profile is very straightforward, but does not have to be necessary e.g. when you use IMAP protocol and have all you messages in your mailbox on the mailserver.