BEFORE YOU COMMENT ABOUT HER APPEARANCE PLEASE READ THIS.
 
I decided to be unique with my Firefly design for once and break the trend of Dash recolors, again. So I looked up Firefly on the MLP Wiki and came to the realization that most G1 ponies have about fifty GAZILLION variants for different countries, which means that while in most countries, Firefly was pink with blue hair and most often blue eyes, some countries had orange, blue, turquoise, or even yellow hair. So instead of going for the one everyone uses, which is completely overdone, I went with my very favorite Firefly variant, the Mexican variant. So yeah, she looks nothing like most depictions of Firefly, and she’s still completely within reason. Why should I limit myself to just the same old blue and pink pony when I could use the pretty rainbow one? There’s no rule against it!  
General Firefly was the leader of Cloudsdale when the Everlasting Night came about, and at the time, while ponies lived in harmony under Celestia and Luna, they were very segregated and the traditions of each race tended to make the gap even more, so generally ponies had no idea what was going on in the other communities; Pegasi paid attention to Pegasi news and Unicorns paid attention to Canterlot news, so on and so forth. Sure, Celestia had news that everyone paid attention to, but she was the Goddess of the Sun, and she was all three races in one, so she clicked with everyone. Every race considered themselves the closest to Celestia. The unicorns argue that her magic made her close to them, the pegasi considered her wings a representation of the sky and therefore closer to them, and Earth ponies saw her strength and how her sun directly helped them with their crops. I’m getting off point, I just wanted to explain a bit of the pre-NMM climate of the world.  
The night that Nightmare Moon took over actually lasted far longer than Twilight’s memory we saw on the show would suggest. The potion Zecora gave her is meant to condense history into its basic moments for teaching purposes. It’s only meant to go back about a century, or give very vague depictions of events farther back, but using Twilight’s Alicorn magic, she was able to extend it into the far past. So while it appeared to her to be a short fight after Luna was transformed, in reality it was almost ten days (or what would be days) of fighting, Nightmare Moon and Celestia chasing each other across Equestria as their magic ravaged the land with their lasers and sheer raw magic power. The only reason that all life didn’t end was that Equestria doesn’t work like ours and the Hearths Warming fires were still going strong. All three races watched in awe and horror as Celestia and Nightmare Moon were caught in what seemed to be an endless combat. The Pegasi found that the cold was freezing their clouds and causing them to fall, and soon Cloudsdale was to crash into Canterlot. What happened instead was that the unicorns of Canterlot banded together to slow the fall.  
The three races worked in harmony that night, Pegasi actually got their reputation as messengers during that week, as they flew to every settlement they could to tell them to make the pilgrimage to Canterlot, when they got there, keeping themselves warm as they prayed that the night would end. General Firefly was in charge of keeping the fires that the unicorns set going, which ended up saving many ponies, although unfortunately there were many settlements that froze because they had no idea what was going on. But they survived, and when the night finally ended, Celestia asked the ponies of Equestria to form the E.U.P, and everypony unanimously decided Firefly was the pony they should select for the Pegasi regimen.  
For the first year of Celestial peace, the entire world celebrated, and Firefly selected an elite team of potent magical pegasi and on the first day of the week long festival (which eventually was cut down into one day) they flew around the world, Firefly performing the first Sonic Rainboom. When they finally landed back down in Canterlot, the sheer amount of ambient magic that they had collected due to the joy and energy the ponies they flew by caused a massive explosion of magical lightning that rained down from the path they took. They soon formed the Wonderbolts, and Firefly lived a long life, performing every year at the festivities until she was too old for it. She had four daughters with a pegasus she had crashed into while practicing for the festival during the seventh year that they did it. These four daughters descendants are the four main houses of Pegasi; the Kickers/Doos, Spitfire’s family, Dizzy Twister’s, and Rainbow Dash’s.