That's a printer-specific feature, so you need to set that up in the printer's preferences. In Thunderbird's print (preview) dialog, click the link at the bottom that says Print using the system dialog. You should then be able to select your printer and change the preferences for that print job. For attachments, you will of course open the attachment using a suitable program installed on your computer and use its print function and change the printing preferences for that print job as you desire.

There is no link at the bottom that says Print using the system dialog. So I'm not be able to select printer setup!

You have to open Tbird's Print (preview) dialog first, by clicking the Print icon OR using the Ctrl-P keyboard shortcut.

I have opened the print-preview(attachment)....but there is no link at the bottom!

That is NOT the print preview dialog. You are viewing a pdf file using Thunderbird's inbuilt pdf reader!

Clicking the Print-Icon directly starts printing !

Clicking the Print-Icon directly starts printing !

You should be getting a preview, as shown in the attached image. Open the Config Editor and search for the preference called print.always_print_silent. If it's set to true, toggle it back to false, which is its default value. As far as I know, this controls whether you get the preview dialog or not. Setting it to true has the effect you're experiencing, that is, print jobs are sent directly to the printer as soon as you click Print, as its name suggests. Restart Thunderbird after the changes.

Thank You! This hint resolves my problem(attachment)!