In most cases (if you make enough money), you should never stop maxing tax-deferred accounts if you intend to FIRE.

Let's assume for a moment worst-case, and you'll never be able to put any money in taxable. Let's also assume combined federal and state tax bracket of 25% (22% + 3%). Finally, let's assume you're married, and your household expenses in FIRE are $50k per year.

If you put money in taxable, you pay 25% now plus dividend drag (~0.3%), but capital gains would be exempt when you retire so there's a plus. Meanwhile, in the 401k, you pay your annual expenses (whatever those are) plus 10% penalty plus your effective tax rate after you retire. This effective tax rate would be 0% up to the standard deduction of $24k, plus 10% for the next $19k, plus 12% for the next $7k, which works out to an average of 5.5% (plus a similar reduction for state, let's say 1.5%). So ignoring annual expenses, if you combine the effective tax rate with the penalty, you're still only paying 17%, which beats 25% any day.

But, this is all academic, since if you're FIRE and you truly have no taxable with which to do a Roth pipeline, you can do a SEPP, which would completely avoid a penalty.