Steps 1: It could be generall issue with firefox.. Plz try to perform cleaning cookies and cache. step 2: Then try to restart. if you still face the same problem try to create to run firefox by disabling the addons. Step 3: Check if you are able to watch on youtube if you are not able to play videos on youtube also please check if there is adobe flash player is installed properly or not. To verify flash player plugin : https://www.adobe.com/shockwave/welcome/ if it says flashplayer is working fine. Step 4: Create another profile by clicking on menu next to the tool bar and click on " ? " next to customize from the menu. choose the option "restart firefox without addons disabled. " Make sure you take backup of the profile and bookmarks this process automatically takes backup or prompts you to take a backup. And creates a backup folder. If still not resolved try to reinstall firefox. NOTE: Make sure you take backup of your passwords stored and bookmarks, favorites.