Is there a way to get this working on Thunderbird? When I right-click on the email message window, the popup menu doesn't include the usual Mac items (Substitutions, Transformations, etc…)
Unfortunately it's not possible. The additional text field options are available to programs that use the Cocoa APIs to interface with Mac OS X and Thunderbird doesn't use them (part of it's cross platform compatibility choice).
You can however use an alternative program such as TypeIt4Me or TextExpander which will work with every program instead of just those that leverage the built-in features of Mac OS X.