The start page appeal to donate can’t currently be turned off. If you like, you can change the start page to something else. To do this, in Thunderbird go to Options | General
Akka tura, tiɣri i tewsa ɣef usebter agejdan ur yezmir ara ad yens. MA tebɣiḍ, tzemreḍ ad tbeddleḍ asebter-ik agejdan akken ad tsekneḍ ayen-nniḍen. I waya, ddu ar Iɣewwaṛen | Amatu