i have had the problem of my safari after numerous updates not being to play embedded content it got in the way so much that i a pretty hard apple fan turned to google chrome as my default and become rather seasoned in it's use then one day i was today i'm going to have another try and after seeing that mountain lion hadn't changed anything i removed all my extensions i had installed and thought since Lion things like Safari rarely properly quit so maybe with all these extensions and a proper reboot maybe what it's needed all the time so looked it up and opened up Terminal /Applications/Utilities or just use spotlight open the application and type in sudo killall Safari if gives you warnings and asks you enter your password enter it and press enter however nothing will show onscreen then it should be fully shut down launch it again and my problem of several months had disappeared 
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