Doation request will n ot go away after making a donation.

Thank you for the donation, the developers will appreciate it.

A screen shot from you would be helpful so we can see exactly what you're talking about, but I will guess you're referring to the attached image. That's known as the "Start Page", and you can turn it of in <Settings | General | Thunderbird Start Page>. Just un-tick the "When Thunderbird launches, show the Start Page" option.