And in my case I would consider double my donation this year. Because we need them and alternative browsers more than ever, because current Tech landscape dramatically need more ethics and less golden boys.
IANAL, but I don't think companies can ask for donations. You'd need to donate to the Mozilla Foundation, which is not in charge of Firefox. I believe you'd have to purchase a product from the Mozilla Corporation, though that product doesn't have to be the browser itself.
They added a new explanatory line to the 2018 form 990. It clarifies that the compensation comes from the subsidiary. That seems quite odd to me, but at least it isn't eating the foundation's budget.