perhaps you need to get some context and you might understand.

Click in the header of a received email to get the menu your talking about trying to find in the compose window.

Just a wild guess, but have you turned off the contact pane by pressing the F9 key. (it turns it on and off)

Contact pane is still there but I still can't find 'save recipent's addresses' - and you're right. I don't have the context!

Do you have it now. The star is where to click. First time is changes colour and adds, the second time the window opens to allow basic editing. Or you can click the edit button to do a full edit of the contact.

Thanks for the detail Matt. I've done that and where it says address book I've made my address book default and clicked done. It still opens up with 'All address books'

Not sure if this will help but if you open Address book, right click the folder you want to be your default address book and click "Default startup directory" that changed it for me.

Many thanks Fergus - finally solved.

This does not work as intended on my setup. Manjaro Linux XFCE 4.16 with Thunderbird 91.6.1.

I want to use something else than "My Personal Address Book" as default, so I opened the Address Book window, selected the preferred account and chose "Default Startup Directory". See screenshot 1.

This, however, has zero effect on where addresses go by default when clicking the star in the header panel - they are always put in "My Personal Address Book". See screenshot 2. I have to click again to edit the contact to be able to save the address in my preferred book.

I tried searching in Advanced Preferences. Most of the hits when searching for "address" pertain ldap settings and of those that don't none seem to deal with default locations.

Thankful for any input on this.