The new 200cc mode that came to Mario Kart 8 recently has nerfed the firehopping tactic.
Firehopping, a tactic known by Mario Kart 8 players that lets you go faster during a boost by hopping right and left while using the drift button has become irrelevant with the 200cc mode. Pulling firehopping off would usually give the one doing it a speed advantage.
We don't have video of the nerfed effect, but many reports on NeoGAF and other places seem to agree.
The nerf seems to only apply to those playing the game in 200cc mode.
Thanks, Nintendo Life.