What securities does Mozilla have investments in?
I only have the answer to why they have investments. Because they have a significant amount of money on hand, and are holding it in the way that makes the most money for a project. When you put money in a bank, they invest it too. This way generally makes more money than interest from the bank.
What Central American/Caribbean securities or hedge funds does Mozilla invest in?
Don't know that either, but I can say why they do it. Diversification of your financial holdings over multiple currencies and over multiple national economies protects you from a crash in a single economy. The reliability of the US economy is no sure thing at the moment.
Why does the Foundation license its trademarks to Mozilla Corporation, its wholly-own subsidiary? Is that normal?
Yes. In this case I think it's a difference in tax status between the non-profit and the operating company. Sometimes it's done to keep the trademarks from being assets that could be placed in peril in a lawsuit. For-profit entities sometimes offshore the intellectual property rights as a tax shield, but I don't think that's happening here.