Try to reinstall your flash player. https://get.adobe.com/en/flashplayer/?no_redirect Hope this helps you.

This could be related to YouTube now serving the HTML5 player to Windows XP users instead of the Flash player. If you right-click the player area, and look at the last line of the short context menu, does it indicate HTML5 player or Flash player? (If Firefox's regular context menu appears, press and release the Alt key to clear it.) If it's the HTML5 player, here are two possible workarounds: '''(1) Use an add-on to force YouTube to serve you the Flash player''' There are at least two extensions for this, you only need one: * https://addons.mozilla.org/firefox/addon/youtube-flash-video-player/ * https://addons.mozilla.org/firefox/addon/youtube-flash-player/ '''(2) Use an add-on to tell YouTube you're still running Firefox 39''' (A) Install the extension https://addons.mozilla.org/firefox/addon/ua-site-switch/ which admittedly has a confusing interface. (B) Select and copy the old user agent identification for Firefox 39: <code>Mozilla/5.0 (Windows NT 5.1; rv:39.0) Gecko/20100101 Firefox/39.0</code> (C) While on a youtube.com page, click the little drop-down triangle for ua-site-switch and paste the old user agent string and then press Enter to save it (D) Then reload YouTube bypassing cached files (Ctrl+Shift+r) (E) Repeat B & C on https://www.youtube-nocookie.com/ to apply the hack to embedded videos