Go to the main Thunderbird view and click the Write option to open a new message.When you have finished creating the signature, copy the HTML code from the signature generator and paste it into the Signature text section in Thunderbird. Note: Instead of composing your email signature in the email body, you can use this email signature generator, which really simplifies the process. Please make sure that the Use HTML box is checked. In the Account settings window, you need to paste the copied HTML code into the Signature text section.(to see a more detailed instruction on how to access them, please refer to step 2 in the previous method). Copy this text and click Cancel as we do not want it to be inserted at this moment. In a new pop-up window, you should see your signature in form of HTML code.Once the whole signature has been selected, go to the Insert tab and then click the HTML… option.You can do that by pressing the combination of Crtl+A on the keyboard or going to the Edit tab and then clicking the Select All option. Once the signature is composed, select all in the email body.In the new message window, you can compose your email signature using a basic toolbar or, to adjust it to your needs, you can use available formatting options under the Insert and Format tabs as well.Go to the top menu and open a new message by clicking the Write button.Are you looking to create a 'fancy' signature in Thunderbird with various font sizes, colours & styles? Also want to include your company logo?

Thunderbird insert signature shortcut