I think, it's blown way out of proportion, like most criticisms of Mozilla are.
It's not like they're actually endorsing cryptocurrency, it's just their usual non-profit call for "if you happen to have too much money, please gib money".
Besides, Mozilla is a privacy-adjacent organisation. Cryptocurrency is horseshit for the environment, but it is a useful tool for anonymization.
And I have a feeling that people wanting to make a donation to Mozilla are largely not going to be the egoistic wealth chasers, but rather privacy-minded people that would prefer to stay anonymous as much as possible. I don't think chewing those people up over their environmental impact is good.