Whatever a floor monitor is, smoking is always a bad sign.
I'm going to guess you're talking about a floor standing hifi speaker. Smoke can only really be you turning up the volume too high. You may need to replace the main drive unit -- the test is whether the drive unit rustles if you (gently) push it in by hand.
The rustling would be the varnish from the coil's wire has boiled up -- thus the smoke.