How to disable URL sharing

On macOS High Sierra (perhaps also earlier version of macOS), I noticed that when I open a URL in a webbrowser (tested with Safari and Opera), that on other Macs in the local network, the Docks shows an additional icon of the local browser on the left hand side. When I click this icon, it opens the URL that is open on the other Mac.

I have three questions: How does this (technically) work, how is this feature called, and how do I disable it?

As for the technology, I assumed that the URL of the frontmost browser window would be shared using a discovery service (DNS-SD, formerly Bonjour), but I couldn't detect it with a Bonjour browser. My second thought is that it is some kind of AirDrop technology, but I couldn't find it there either. So I'm not sure if this is sharing on a local LAN, or sharing using the same iCloud account.

It's called Handoff & is part of Continuity, enabling seamless working between all your devices.

As far as its underlying structure, Continuity uses Bluetooth, WiFi & internet connectivity, all linked via your iCloud account.
Handoff itself requires Bluetooth, so works at short distance only.

Turn Handoff on or off

Note: If you don’t see a Handoff option on your device, it doesn’t work with Handoff.

• On your Mac: Choose Apple menu > System Preferences, click General, then select “Allow Handoff between this Mac and your iCloud devices” (below “Recent items”). To turn it off, deselect the option.

• On iPad, iPhone or iPod touch: Go to Settings > General > Handoff, then tap to turn on Handoff. To turn it off, tap the option.

• On Apple Watch: Open the Watch app on iPhone, go to My Watch > General, then tap to turn on Enable Handoff. To turn it off, tap the option.