Google will be taking another step towards an HTML5-only Web later this year, as the systematic deprecation and removal of Flash continues.

In a plan outlined last week, Flash will be disabled by default in the fourth quarter of this year. Embedded Flash content will not run, and JavaScript attempts to detect the plugin will not find it. Whenever Chrome detects that a site is trying to use the plugin, it will ask the user if they want to enable it or not. It will also trap attempts to redirect users to Adobe's Flash download page and similarly offer to enable the plugin.

There will be a few exceptions to this policy, with Google planning to leave Flash enabled by default on the top 10 domains that depend on the plugin. This list includes YouTube, Facebook, Twitch, and Amazon. Even this reprieve is temporary. The plan is to remove sites from the list whenever possible—Twitch, for example, is switching to HTML5 streaming, so should start to phase out its use of Flash—and after one year the whitelist will be removed entirely. This means that after the fourth quarter 2017, Flash will need to be explicitly enabled on every site that tries to use it.

For enterprise users, Google will add support for managing the whitelist to ensure that corporations that need Flash for intranet sites will not suffer any problems.

Flash is already the last remaining plugin, with every major browser now severely restricting, if not outright prohibiting, any other plugins. Browser developers are now consistent in their desire to push it off the Web, but its wide use—and the complexity of many sites that continue to use it—means that this still isn't a straightforward proposition. Complex content such as browser-based games can't readily be converted to HTML5, so even when Flash moves to a disabled-by-default model, it is likely to remain a feature of browsers for some time yet.