There are several steps you can try to clear up the problems.
1) First, try to restart your browser by shutting it down and then re-opening the browser.
2) Make sure you have the latest version of the browser. Usually you can do this from the About screen. For example, in Firefox, at the top of the screen to the left is a choice called “Firefox”. When it’s clicked, you’ll see “About Firefox”; clicking that will pop open a window that details what version of Firefox is running and if it is up to date. Be sure it is the latest version.
3) Try another browser. For example, if you normally use IE, try using Chrome, Firefox or Safari. Sometimes switching browsers brings the game back to life.
4) What version of Flash are you using? Go find out and upgrade to the latest: http://www.adobe.com/support/flash/downloads.html
5) If you are on Facebook in secure browsing mode, switch out of secure browsing