Now that we know what "sandboxed" is read this good news about Flash Player found by Jim Hamm here: http://appleinsider.com/articles/13/10/24/adobe-confirms-flash-player-is-sandboxed-in-safari-for-os-x-mavericks-
You Can Sandbox Flash Player
You can Sandbox Flash Player in Safari for OS Mavericks as described and explained in this article http://techland.time.com/2013/10/24/finally-you-can-sandbox-flash-player-in-safari-for-os-x-mavericks/
What’s an “app sandbox?. Here’s Apple’s guide to this protection for your security. https://developer.apple.com/library/mac/documentation/Security/Conceptual/AppSandboxDesignGuide/AboutAppSandbox/AboutAppSandbox.html
Sandboxing, Pro and Con
Have you seen the term, "sandboxing" yet? To keep up with the new terminology look at the February issue of MacWorld, pg. 14. A longer version of this article is on their website. Here, 31 comments help round out the view, pro and con, of this restriction on developers of new apps.
Sandboxing: What? Why?
Maybe you've already heard the word, "sandboxing." Jim Hamm finds something that explains it. He writes, "Sandboxing is here in Lion, and soon will be for apps as well. A prime example of Sandboxing in Lion is that Safari no longer connects directly to the web. Another process does that. Sandboxing is meant to be an additional security for a Mac user. I think this is a good step by Apple, but there are other thoughts on this. Here's an article that provides further insight into Sandboxing."