> The economics of selling branded clothing has been very well understood for 50 years. The markup for slapping a logo on a T-shirt is massive. Plus, it's a form of crowdsourced, word-of-chest advertising.

None of that addresses the point that the old logo was already very merchandisable.

Furthermore, whatever markup they’re making is not something you can just generalise. It is very possible, likely even, that the bulk of the cost goes to whatever company is making the t-shirts (I haven’t looked but I doubt Mozilla is doing it in-house).