It's weird that when I tell my kids that when they want to help, but they won't help in the way that someone needs help, that they aren't actually helping, they understand it.
Mozilla has buckets of money, between the Corporation and the Foundation. They are separate, for good-ish reasons? But they are separate. If they start allowing customers or businesses to pay for Firefox, then they will have to provide an entirely different level of support. They will need a billing and support team that is beholden to those paying customers.
It will shift the focus that Firefox has on attracting and retaining users to attracting and retaining paying users.
It will mean they need to meet various warranty and regulatory requirements around the world, and potentially introduce new business risks and liabilities related to those requirements (e.g. non-compliance with specific regional legislation).
What you are asking for is to pay Mozilla for Firefox, and to get there you need a radical shift in the organization that supports and ships Firefox.
Or, you could do what the rest of folks who want to support Firefox do, and make a donation in the way that Mozilla is signalling is the best way to support Mozilla's mission and Firefox development.
If that isn't good enough for you, track down an OSS contributor to Firefox, and give them money. Direct action for the win!