Well, when I installed IE8, it requested to run add-ons on websites:

On some web-sites I ran this add-ons:

but, when I run add-ons IE displays Security Warning:

I have already installed Adobe Flash Player 10 ActiveX and Adobe flash player plugin, but I think one of them is Opera's

Which of them should I run? Run add-on on each website or run add-ons on all websites?

Since updating IE you might have to reinstall. Have you tried to reinstall it?