adobe flash_player has just under three hundred CVE entries for software flaws. (note to pedants: the NVD search includes GNU bullshit clones if you run a simple search on 'flash player')
apple quicktime has over two hundred -- and that's ONLY counting from OS X days (i.e., not including Mac OS days).
Writing network-enabled rich-content delivery platforms is a hard task. flash player is installed on a tremendous number of devices across a staggeringly diverse operating system segment. Problems are sadly impossible to avoid.
Firefox has more than 1100 -- again, not counting Mozilla days. Chrome has more than a thousand. Safari, commendably, has little more than five hundred. The point is nobody gets it right. Not even Steve Jobs.