Windows 7: help with youtube videos

when i use firefox 4 rc or google chrome 11 latest, i get problems with youtube videos. When i switch them to 720p or higher the video freezes but the sound continues to play. I tried this in ie8, and its fine there. Both my adobe flash active x and plugins are the latest 10.2.152.32. What could be going on? Should i be concerned since they are both not the final stable versions? If not how do i fix this?

Firefox 4 RC is not a final version and Flash player is a boulet for internet. You can try to re-install the flash version of firefox, you can also try the HTML5 version of youtube YouTube - Broadcast Yourself.