Unable to watch YouTube videos in Mozilla

When I trying to watch youtube video which is available on UP Police Admit Card 2014. It's showing that flashplayer is not installed, when we start to install flashplayer then it's show install manually. I try to download and install manually. But I always unable to install flashplayer install for Mozilla browser while the video is best working in Chome. I have Windows 8.1 installed on my computer. Please help me, if it's possible to install it on my computer.