Is this how this word is normally used - in plural, like in English? In my native language we use the singular, fyrverkeriet in this case and -er(na) would have meant several of the kind...
I can't really imagine ever using the singular here, but I suspect there's large variation. Other people do use the singular. Either typically works like you say English does.
It's actually pretty often used simply as "fyverkeri" - firework(s), as "fyverkerierna" would be "the fireworks"
Just to clarify, is this one of those ett words that pluralise like en?