Could someone explain the difference in chemical makeup between an ordinary fluorescent light that has been in wide use for more than 50 years and a compact fluorescent light? The chemical makeup of the fluorescent light must include the ballast.
A 50-year-old fluorescent light fixture would have the ballast encased in a metal box; the fixture itself would likely be made of metal. In case of a critical malfunction the ballast might catch fire, but the metal enclosure would most likely prevent it from igniting anything else. The ballasts 50 years ago didn't often didn't contain any fire-retardant chemicals, but the metal enclosure would mitigate fire risk. Note that such fixtures often had a three-prong cord, with the ground terminal tied to the metal case, to prevent a shock hazard in case a failing ballast developed a short between the live wire and the case.
Newly-manufactured fixtures use electronics which are more energy-efficient than the classic ballast, but are also more prone to exothermic failure. Although some full-sized fixtures may still encase the ballast in metal, many instead rely upon fire-retardant plastics. Although flame retardant plastics are often effective at preventing fires, many of them work by outgassing nasty fire-suppressant chemicals when heated. This would be great if the plastics only outgassed the chemicals in situations where they would otherwise burn. Unfortunately, the plastics will outgas the chemicals (albeit more slowly) when they are heated to a point well short of combustion; some CFL electronics get hot enough to cause such behavior. Not only do the released chemicals pose health risks, but the fact that they've been released can render them ineffective in preventing fires. A lamp which develops a fault which causes it to run very hot for a few months but still work apparently normally could burst into flames if a more critical fault occurs.
It might be logical to require CFLs to shut down or switch to an intermittent mode of operation if they get hot enough to cause outgassing. Unfortunately, that would give CFL's an even worse reputation with regard to reliability.