Signature Switch is one of great Thunderbird Add-ons, it lets you define several eMail signatures and easily select them via a toolbar-button or shortcut key or context menu!

You may use in your signature some styling, in case you write html and not simple text messages. However, there is a problem with the “font-family” CSS directive, Thunderbird won’t obey it! No matter how you define it, in a div tag, in a table style, even in a href tag style, Thunderbird ignores this property!

The only solution that I’ve found is the use of the old font face html tag. Enclose your plain text line or even link inside this <font face=””> tag, and Thunderbird will follow it and will display your line or link in the font family you selected. You can also define several typefaces in the same tag. Here is an example:

<font face="Segoe UI, Verdana, Arial"><a href="https://www.thefreewindows.com/" target="_blank">TheFreeWindows</a></font>

Enjoy!