I had a project to design a Flash component API that needs to be easy to integrate with all video players. I had investigated more than a dozen video players used by web publishers of any size. These video players included big brand names like YouTube and Brightcove, and generic players such as JW and Flowplayers. The goal is simple: the Flash component API needs to work on any given web pages. Making jobs easy for other developers means we have to do all dirty works.
More than once, I found my Flash component failed to load on IE. It's always perfect on Firefox. It also happened only on a few sites.