Which screen are you referring to? The Start Page within Thunderbird itself? That can be disabled in <Settings | General | Thunderbird Start Page>. Or the one you get after initiating the installer download from the Thunderbird web site? That one can be dismissed by clicking on the X in the upper rig (see attached image). The download will still proceed whether this screen is displayed or not. Be aware that this screen is a suggestion only, that Thunderbird is free to download, install, and use.