I just started using the Thunderbird Windows platform. In this current version of Thunderbird, I've noticed that the software doesn't provide us with suggestions while writing the recipient's email ID... I mean, we do have an option to save contacts and fetch accordingly later. But to be honest, saving contacts for a temporary email is not worth the time (temp emails: those emails to which I send emails rarely or in some situations when I need them the most, like customer care emails).
Therefore, Thunderbird should suggest the recipient's email ID when I start to write them on the 'to' bar. This would be more convenient, rather than saving them as contacts.