Developer Console

Run JavaScript on any page, live. The DevTools inspector includes a console REPL with a few party tricks.

Open it

Quick Tools → Dev Console, or Ctrl Shift I. You’ll find four panels, including the console.

The REPL

Type any JavaScript and it executes in the current page’s context. Results print inline. It’s backed by GeckoView’s console output (consoleOutput(true) on the runtime).

Quick actions

Toggle contentEditable — make the whole page editable (pairs with Page Editor).
Inspect element — peek at the DOM under your finger.
Read network/log output — see what the page is doing.

A real console, not a toy

Because it runs in the page’s actual JS context, anything you can do in a desktop DevTools console, you can do here — including debugging your own sites on-device.