How to block all websites except one in Chrome and Firefox

The Internet is an overwhelming source of information, but it also has many equally overwhelming distractions. Staying focused on the web is far from easy, so the desire or outright need to block websites is quite common. Besides the distractions, there are safety reasons. There's a ton of disturbing content, and maybe you're a concerned parent. Whatever the case, there are … 

How to block all websites except one in Chrome and Firefox

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