Mirage Dragon only prevents Traps from being activated. It doesn't prevent the activation of Trap Effects. It won't prevent Navigation's negation. Nor will it stop the effect of something like Skull Lair or Des Counterblow.
Ok, so what would be a definition of Trap being activated, and a definition of Trap effect being activated ?
Is it :
Trap activation = flipping a face-down trap (regardless of its location, hand/grave/field).
Trap effect activation = using the effect of a face-up trap (regardless location)
?