start firefox at 1024x768 resolution
    
    when we run firefox in a bare X session, by default we get an
    800x600 firefox in a 1024x768 X server with some dead black
    space to the right and bottom of the screen. Now it turns out
    that if the mouse is in the dead space, Firefox will not get
    any keystrokes we send.
    
    This didn't used to be a problem, but I made it into one with
    this os-autoinst change:
    
    https://github.com/os-autoinst/os-autoinst/pull/559
    
    that makes os-autoinst move the cursor to 1023,767 after each
    `assert_and_click`, instead of 0x0 as it did before, unless the
    cursor has previously been explicitly place somewhere. So in
    this case it gets moved to the dead space, and Firefox stops
    responding to keypresses after the first `assert_and_click`.
    
    We could equally well fix this by setting the cursor to 0,0
    after running Firefox, but I like this more as it makes sure
    we won't run into the same problem some other way, and makes
    the videos and screenshots look nicer.
    
    This fixes the realmd_join_cockpit test that's been failing
    ever since I installed an os-autoinst with that fix. Committing
    without review as it's a straightforward fix and I want the
    test working again...