Excuse me for being a Trek nerd. The Ferengi were first introduced in The Next Generation. A big point was made at the time that these aliens had never been seen before. And, lo and behold, they show up in Enterprise. I didn't watch enough of the episode to see what kind of retconning they did to justify it, but I don't care.
It's just another sign of the laziness and ineptitude on the part of the writers and directors that caused me to give up on watching the show in the first place. They don't trust themselves to come up with anything original or interesting, so they have to fall back on the old faithful "these guys worked in the last series". If they hired decent scriptwriters, and gave them free rein, perhaps they wouldn't have to wave goodbye to continuity? Gutless and weak.
