All of them? Marijuana is still a schedule 1 substance

When purchasing a firearm, that is one of the questions in the Federal application, and you're not allowed to lie.

The federal application for a Federal Firearms License, the license needed to be a firearm vendor, not the (as far as I can tell) non-existent federal license to own one?

It isn't just FFLs. The Gun Control Act (GCA) defines a list of people who aren't allowed to ship, transport, receive, or possess firearms of ammo. This includes any person "who is an unlawful user of or addicted to any controlled substance (as defined in section 102 of the Controlled Substances Act, codified at 21 U.S.C. § 802);" [1]. Since cannabis is federally illegal still if you use it you can't legally even possess (not just own) a firearm or ammo.

I think it is a stupid law though. Imagine if we applied that logic to other constitutionally protected rights. "Anyone who is an unlawful user of or addicted to any controlled substance shall not have the right to vote" or "Anyone who is an unlawful user of or addicted to any controlled substance shall not have the right to due process".

[1]https://www.atf.gov/firearms/identify-prohibited-persons

Admittedly, it's hard to kill another person by voting, or receiving due process. And we do restrict speech when it verges on violence (imminent lawless action, fighting words).

But when people do succeed in killing others through the vote, it's usually a LOT more than they could have ever hoped to do with a firearm.

> Admittedly, it's hard to kill another person by voting

I'm not so sure about that.

> "Anyone who is an unlawful user of or addicted to any controlled substance shall not have the right to vote" or "Anyone who is an unlawful user of or addicted to any controlled substance shall not have the right to due process".

Not the same thing at all, because a firearm is directly and irrevocably more dangerous while under the influence of drugs.

You can debate the tradeoff of "right to bear arms" vs "right to regulate arms" (just as voting has gone through lots of regulations, some terrible (black people, women), some OK or debatable (showing proof residence or citizenship somewhere in the process), but it's not obvious simply by analogy to other rights.

There is no “license” to own or possess a firearm, parent is referring to the Form 4473, which is used to conduct a background check via NICS.