Can't get firefox to render the right size in a headless xvfb instance

Question

I can start the xvfb instance just fine

Xvfb :1 -screen 0 800x600x24

I can then launch firefox and have it load correctly but the window is always smaller than the resolution I set during the xvfb command.

firefox http://www.ebay.com --display=:1

You can see the black bar, that's the full resolution. It appears it's sizing to what the page wants but it will never fill it out completely.

Answer 1

Here is a solution, not pretty but works. Uses xdotool to set size after Firefox is running.

First:

xdotool search --onlyvisible firefox

This will display a single window ID, windowid. Then:

xdotool windowmove windowid 0 0
xdotool windowsize windowid 1280 720

You must first do the windowmove and follow it by the windowsize.

In some cases once I did this, the size and position were correct forever more, in other cases had to run again each time I ran Firefox.

Answer 2

Assume the border is there and compensate accordingly in your capture. If you need 1024x768, then set the screen size to 1034x778 and capture 1024x768

Xvfb :1 -screen 0 1034x778x24 > /dev/null &
ffmpeg -t 1 -s 1024x768 -f x11grab -i :1.0+10,10 -f mjpeg screenshot.png