Learn Swedish: Du får inte stirra dig blind på chokladfontänen. - You must not stare yourself blind at the chocolate fountain.

It combines the verb stirra (stare), the reflexive pronoun dig (yourself), and the adjective blind (blind). In these constructions, the adjective describes the state you end up in as a result of the action. You aren't staring "blindly" (which would be an adverb); you are staring until you become blind to other things.

Is stirra sig blind meant literally here?

No, it is a very common idiom! Att stirra sig blind på något means to focus so heavily on one specific detail that you lose perspective and miss the bigger picture. The speaker is telling you not to get so obsessed with the chocolate fountain that you ignore the rest of the event.

If the subject was plural (ni instead of du), how would the phrase change?

Both the reflexive pronoun and the adjective must agree with the new subject. For the plural ni, the pronoun becomes er and the adjective takes its plural form, blinda. The sentence would become: Ni får inte stirra er blinda på chokladfontänen.

Just as a refresher, doesn't får inte mean "don't have to"?

No, that is a common trap! Får inte means "must not" or "are not allowed to"—it is a prohibition. If you wanted to say "you don't have to," you would use behöver inte or måste inte instead.