Whoa. This was interesting.
OKAY, explanations aplenty. Back in the eighties, there were two major canons for the G1 ponies - the US cartoon and the UK comic books. Like all things back in those days, depictions between countries would sometimes vary wildly for the same character, due to no universal character bible. Luckily, stuff like this doesn’t happen anymore - or maybe unluckily.
1) Firefly, wonderful and badass as she was in the US, was actually headstrong to the point of being an idiot in the UK. She’d do anything if it gave her a rush, even if it resulted in her holding the Idiot Ball. It was up to her best friend Medley, who was smart and secure, to rescue her most of the time. G4 Rainbow Dash seems to be a balance between both versions.
2) Twilight’s personality in the UK was much more of a drifter than the US version, preferring isolation. She made very rare appearances and was always quite mysterious. Whenever she did appear, it was usually only because her magical powers were required. Reminds me of a certain G4 zebra rather than Twilight Sparkle, who’s now very eager to learn about friendship.
3) Applejack was the same as she was in the US cartoon… incredibly clumsy. She was also a dope. However, she sorta Forrest Gumped her way to victory, with her silliness resulting in the day being saved. This personality might (unfortunately) have something to do with Applejack being blonde… Thankfully, G4 Applejack is the most stable pony, in every single way.
4) Posey has always been the same no matter where or when she was, I guess. She was the gardener of the franchise, and always rather shy and demure. Fluttershy isn’t any different, except now her love is animals rather than flowers.
5) Sparkler was a magpie. Sparkler, you see, absolutely loved jewels and gemstones of absolutely any size - not to mention shells and other pretty rocks. Yep, she was a collecter. She wasn’t so selfish as to hoard her collection and fend off others, though. Rarity’s similar in that she does collect jewels, but it’s because she so easily gives them away as well that makes her the Spirit of Generosity.
6) And finally, Surprise. Pinkie Pie’s current incarnation is identical to the US version of this character. In the UK, however, Surprise was softened down to a more tolerable level - she retained her fun-loving personality, but she wasn’t so intruding of other people’s personal space. She sort of had a special relationship with balloons more than any other party gear.
<3 History lesson!