Take a full page screenshot with Firefox on the command-line

I'm running Firefox on a Xvfb in a VPS. What I want to do is to take a full page screenshot of the page.

I can redirect Firefox to particular page using

firefox http://google.com

and take a screenshot (inside X) using ImageMagick

import root -window output.jpg

The problem is, most of the page need scrolling and I can't know the height beforehand.

The other way is to pick a very big height (like 4000px) and then process the image and remove the useless part. But that's unnecessary processing.

I found many Firefox add-ons, but I'm looking for a solution that can be programmed using the Shell Command line.

Edit: I ended up writing my own FireFox extension for doing this.

Solution

The Developer Toolbar GCLI and Shift+F2 shortcut were removed in Firefox version 60. To take a screenshot in 60 or newer:

press Ctrl+Shift+K to open the developer console (⌥ Option+⌘ Command+K on macOS)
type :screenshot or :screenshot --fullpage

Find out more regarding screenshots and other features

For Firefox versions < 60:

Press Shift+F2 or go to Tools > Web Developer > Developer Toolbar to open a command line. Write:

screenshot

and press Enter in order to take a screenshot.

To fully answer the question, you can even save the whole page, not only the visible part of it:

screenshot --fullpage

And to copy the screenshot to clipboard, use --clipboard option:

screenshot --clipboard --fullpage

Firefox 18 changes the way arguments are passed to commands, you have to add "--" before them.

Firefox 88.0 has a new method for taking screenshots. If extensions.screenshots.disabled is set to false in about:config, you can right-click the screen and select Take Screenshot. There's also a screenshot menu button you can add to your menu via customization.

You can find some documentation and the full list of commands here.

_{PS. The screenshots are saved into the downloads directory by default.}