Are the Fireflies anarchists?

Ellie: "Congrats. One point for the anarchists." Riley: "We prefer freedom fighters." Ellie: (laughs) "Whatever."

No, although they are insurrectionists - which means they use a revolutionary technique associated with anarchists to destabilise hierarchies - unlike anarchists they:

Seek a return to civil government - whereas anarchists want no government.

Ellie: "Did you really leave because you actually think you could liberate this place?" Riley: "Don't say it like it's some type of fantasy, Ellie. They've done it in the other QZs. Set things right, the way they used to be."

They are a hierarchal organisation (with Marlene as the "queen" - whereas anarchists reject all hierarchies.

Anarchism may have 'leaders' in the sense that there may be people who take the lead in the sense of leading people to safety because they know the way, rather than ruling over others and punishing them if they disobey.

"My name is Marlene. I’m the leader of the Fireflies in the Boston QZ."

Also, Anarchists don't tend to mind being called Anarchists, although the word has often been misapplied to those who are not Anarchists.