Maybe @Lusito could share some of his experiences with TypeScript add-on development.
He mentioned one of his add-ons in this topic:
I’m planning to port some of my add-ons to TypeScript, @Lusito could you please share some thoughts about your experience? Maybe some pitfalls to avoid.
Also how did you started your project? Did you configured everything yourself or have you used some generator, like this one: GitHub - phryneas/generator-webext-typescript: generates a basic firefox webextension with typescript support