French language Q&A Forum

Fireworks is translated in this lesson as "le feu d'artifices" but in this page https://progress.lawlessfrench.com/studylists/view/946769 it is translated as "le feu d'artifice". In Larouse online it is translated as "le feu d'artifice" too. The Kwiziq writing challenge about Bastille Day also uses "le feu d'artifice".

But elsewhere on the web I can see examples with "les feux d'artifices" and even "les feux d'artifice". So all 4 possibilities of singlular and plural for both the noun and adjective are covered.

Are all of these variations correct?

Shouldn't "joué" be "jouée," as the subject is elle?

Il aura eu froid cet hiver-là. He will have been cold that winter. Pourquoi on utilise “eu”, Est ce qu’on peut utiliser “ete” C’est a dire, il aura ete froid cet hiver -la