Video Problems

I have Mac OS X 10.5, on a MacBook Pro that was purchased in September 2009. I have had no problems with it, until recently, it seems as though youtube is making my computer act weird. When I go to 'youtube.com' in my browser (Firefox) it will either automatically close my browser, or freeze my browser. When it freezes my browser, my computer isn't even aware that it needs to be force quit; I can just right click on the Firefox icon and quit it like I regularly would. I originally thought that it was a problem with Firefox, so I verified that I had the latest updates and I do. I tried youtube on Safari, and it shows a scrambled picture that you can't make out, will play the sound, and freezes the rest of the browser functions (ie: I can't open a new tab, or hit pause on the video or anything) until I close it by right clicking the icon. This also happened on the Sony website, when I tried to watch a commercial.

The funny thing, is that if I view the youtube video from Facebook, I can watch it no problem -- as long as I don't click the link to open it under a new tab. I have to actually watch the youtube video within facebook. I can still watch most videos that I stream online, from sites such as letmewatchthis.com, and I can watch videos that are on my hard drive through VLC.

I have restarted my computer many times, and I have used my disk utility function to verify my disk permissions and to repair them.

Does anyone have any idea what this problem could be? Or how to potentially fix it? Thanks!