It's probably diatoms. Algae and crud love the rubber from suction cups...that's why I prefer not to use suction cups on heaters, on most of my tanks I just tape the cord to the back of the tank and let them vertically dangle in the corners. I've never had a problem with this approach.
Try wiping the ends of your fluorescent bulb with alcohol and let them dry. There should not be any burning smell, but maybe they got something on them which is burning off at the contact point?
It doesn't matter which light you use since you have no live plants, whatever bulb looks good to you will be fine.