Several changes that Adobe made in Flash 11.3 aim to boost the browser plugin’s security and reduce its susceptibility to attacks. The most significant of those changes is the introduction of sandboxing on the Windows platform.
Due to the frequent discovery of Flash vulnerabilities and the relative ubiquity of the plugin, Flash is one of the most heavily-exploited pieces of software. Adobe and browser vendors have been working to make it harder to exploit by isolating the plugin and working to ensure that users have easier access to the latest version.
Most browsers already implement process isolation for plugins in order to prevent Flash crashes from taking down the whole application. In some browsers, such as Chrome, the plugin is sandboxed on Windows to prevent it from accessing sensitive platform functionality. Adobe has worked with Mozilla to bring that feature to Firefox on Windows.
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Flash player 11.3 will support sandboxing in Firefox on Windows