Turned on furnace & smoke alarm went off!

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My furnace/oil burner have been shut off for the last four months during the summer. Tonight (because of the cool temps) I turned the switches for the oil burner & furnace on, then I turned on the thermostat for heat. After about 5-10 minutes, the smoke alarm in the basement sounded, so I immediately shut off the thermostat as well as the switches for the oil burner & furnace. The smoke alarm stayed on for about ten minutes. While I was in the basement, I noticed some very light puffs of smoke up in the air near the smoke alarm, and I also smelled a noxious odor which made my nose & throat burn a little. By the way, I'm not sure if my furnace is the original from 1957 when this house was built, but it is old...though I had it professionally cleaned last fall.

Is what I described normal when a furnace has been off for 4 months and then turned on? Or is this abnormal, and if so, what could be wrong? I have not turned on the furnace since this episode.