[gorenb]

You could just temporarily turn off the internet. For things like this, you should be using a laptop/desktop instead of a server anyways.

[matusfaro]

Yes, in addition to deleting all browsing data (maybe in a private window) for that site prior to re-enabling internet otherwise the site could store information locally and transmit it once online.

It is time consuming to do this and do it right so I actually already created an extension for it in another ShowHN post: https://news.ycombinator.com/item?id=37469321