Can't view videos in youtube

Since I installed the newest version of safari, I had many issues. It was very slow (even after updating with the new OS version). In a different thread in here, someone suggested to remove my Internet plugins and keep only the default ones

1. Flash Player.plugin
2. flashplayer.xpt
3. nsIQTScriptablePlugin.xpt
4. Quartz Composer.webplugin
5. QuickTime Plugin.plugin
6. JavaPluginCocoa.bundle
7. JavaPlugin2_NPAPI.plugin ?? (This might have been installed by the latest Java Update) ??
8. iPhotoPhotocast.plugin ?? (This I believe is installed by iPhoto) ??

I have the latest Flip4Mac and so I also have these plug-ins:
1. Flip4Mac WMV Plugin.plugin
2. Flip4Mac WMV Plugin.webplugin
3. Silverlight.plugin (This is installed by the latest Flip4Mac on my computers)

With that, I no longer have speed issue with safari. HOWEVER, I no longer can watch video on youtube. Ask me to install the latest version of Flash, which I did a few times. I also reseted safari, repaired the permission and still can't view clips on youtube. BUT, it works in Firefox

I would appreciate some help.

Thanks

-Izzy