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I found some ways to block a specific website such as modifying the host file, using proxy, using browser extension. Is there any better way to block a specific website?
What you're talking about is standard functionality in any proxy server and is the best way to to this.
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how can I track the active time of a tab in any browser?
Define "active time"?
In any case, there's no such thing as a browser plugin that works across all browsers and no consistent way to get at the tabs of each brwoser either. What you're referring to isn't possible unless you write a seperate application/plugin for every browser.