Can't download Thunderbird even though I've donated twice now.

You do not have to donate to download, although the project can certainly do with the funds. The donate page is in the download progression "after" the download is supposed to be initiated in the background. As you appear to be using Firefox, there is a down facing arrow on the toolbar. Click it and see if the download has appeared in the download list. Alternatively as the download usually asks you to click Ok to save the download, your clicking to actually donate might have the request to download dialog hidden behind the main Firefox window, try minimizing Firefox to see if you can get a dialog hidden behind to show up.to