Alongside various new features (Siri, Auto Unlock, Apple Pay) coming in macOS Sierra, Apple’s next major desktop operating system, it also ships with the brand new version of Safari, Safari 10. Safari 10 introduces a major change in the way the browser handles plugins. In short, proprietary plugins like Adobe Flash will be disabled by default when browsing the web.
This means that websites will serve modern HTML5 representations of content as often as possible as they will not be able to detect an installation of Flash at all. Safari is smart however — it will allow you to enable Flash temporarily on demand …
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When trying to view Flash enabled content that does not have a HTML5 version, websites always provide quick links to download Flash from Adobe’s site. With the new plugin behaviour in Safari, the browser will override clicks on these links to show a special new modal sheet.
This sheet allows the user to enable Flash on a per-use basis or enable the plugin site-wide. After confirming, Safari loads the Flash content as normal. This is how popular third-party extensions like Click-To-Flash work. Apple is banking on most websites already having HTML5 versions of content (usually video) available but it is trying to make the less-likely case as inconvenient as possible … only loading Flash lazily when required.
This leads to better performance, better power efficiency and better security by minimizing Flash process usage on the Mac. Similar behaviour has also been bundled for other types of proprietary web plugins, although Flash is by far the most common case. In addition to these changes, Safari is assisting developers with the transition away from HTML5 — adding a few key APIs for functions that previously were only possible through plugins.
A big roadblock here was copy and paste; websites would include tiny Flash applets just to be able to manipulate the pasteboard. With the execCommand API in Safari 10 this is possible in HTML5 standalone.
Safari 10 will be released with macOS Sierra in the fall. Developers can find out more about optimizing websites for Safari 10 on the WebKit blog.