If you want a gentle reminder not to waste time online - without investing in a full-featured paid app such as Freedom - try Nothing on the Internet, an extension for Chrome and Safari that turns off all the content of the web, leaving a zen-like expanse of empty wireframes.
As Fast Company notes, the extension (by the creative agency Sideline Collective) is also a nice web design tool, since it shows off a site's underlying structure. Check out the collective's gallery of popular sites stripped of content.
If you still believe in outdated concepts such as privacy, do note that in order to work, the extension needs permission to track your browsing history. Seriously though, this is pretty typical for browser extensions, and if you want to write to everyone involved and ask them what they plan to do with your data, you can find them here.
This article has been updated since its original publication.