I have Verizon DSL -- the cheap 768 kbps variety -- and I had no problem with streaming videos (Youtube, etc) until recently. Now, it will play for a second or two, pause play another two seconds and so on, as if it has to stop and buffer. I've tried pausing the thing for a minute or two to let the whole thing buffer at once, but no dice there. I've checked all the firewall and security settings in my Norton Internet Security 2009, and I can't seem to find anything that has changed in Firefox 3.0.7. I have plenty of RAM (2GB running WinXP SP3) and an ATI Radeon X300 video card. What can be causing this?

The most likely cause is either the server you're streaming from (it's very busy) or your provider.