There is no donation requirement. You may donate at an amount which represents the value you are getting from Thunderbird on these devices.

Excuse me but there is a minimum donation requirement otherwise I couldnt start the download. What I'm asking is if I'll have to donate to every device that I want to download the program.

Yes, the donate screen has a minimum, and donations are appreciated, but please do not consider the presence of the donation screen as a requirement to donate, or blocking downloads.

Your download should have already completed, without making a donation. Please check your downloads folder.

You do not have to donate (again).

The following link might be helpful: thunderbird download https://support.mozilla.org/en-US/questions/1511753#answer-1732726

Quotation from the above link:

3. After you click "Download" button, the page will show request for donation, but you should find the downloaded file on the top right corner of your browser.

Please see the attached images in the above link.