Adobe Flash Plugin crash

I am trying to watch videos for my online schooling. The video's will not play unless I restart my computer and play them right away. They will usually play until I take a break or pause the video for an extended period of time or until the computer goes to "sleep". At this time, the videos will be frozen and will not play or the entire FireFox browsing window is frozen. I will have to restart my computer again before I can watch any other videos. Someone please help!