User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.0.3) Gecko/2008092417 Firefox/3.0.3 Build Identifier: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.0.3) Gecko/2008092417 Firefox/3.0.3 I was watching a show on NBC.COM in their video player. After it was playing a while, (12-13 minutes), I started getting a warning message that would pop up periodically: Adobe Flash Player 9 A script in this movie is causing Adobe Flash Player 9 to run slowly if it continues to run, your computer may become unresponsive. Do you want to abort this script? Now I know that error comes from the flash player -- and looking at the process with processexplorer, I could see it was spending most of the time in the flash player DLL. However, it was still the case that all browser processes -- including all of the flash player applications would run on the same CPU. Oddly, FF showed 20% CPU usage -- but that's 80% of 1 CPU (4 CPU system). The problem got worse if I tried to open another FF browser window to look at another site while the video was playing in the first window. It would really benefit if plugins, for example, could execute in a separate thread (or process) that would allow them to execute on another CPU than the main browser. Attempting to force everything onto 1 CPU increasingly slows down FF performance as more windows(tabs) are opened. Note -- the Flash player running slowly message, so far, has been confined to the NBC video player. with a 3.2GHz, 2x2-CoreDuo w/4GB, WinXP-SP2, my machine should have more than enough CPU power to play back a video in one window and browse in a 2nd. Reproducible: Always Steps to Reproduce: 1. 2. 3.