Symptom and Solution. On Windows, kept getting auto-started instances program iexplore.exe running. Virus scanning for days didn't solve the problem. Finally a Windows system restore back to November or so did solve the problem.
Larger Solution. Of course, for each video clip on a Web page, Firefox and Flash keep saying that Flash is vulnerable. No joke. Then they refuse to play the video unless I confirm by clicking three times. So, great! Now those videos no longer auto-play.
Of course, for this benefit, I am still running version 12 or some such of Flash. So, after 12 versions, Flash still has bugs? So, I'm going to believe that 13 is such a lucky number that finally version 13 will be safe? Nope! So, I will stay with version 12 and, thus, block the auto-play videos. When I do want to play a video, it will be a significant video from a respected source and, thus, likely safe; I have to doubt that version 13 would be much safer.
There are other such frustrations at Web sites that still cause me to do what you do -- leave!