On my old Thinkpad X200 with Ubuntu/Intel graphics.
Firefox 14. Smooth transition lasting about 1 second. The smoothness suggests more than 4fps. The text within the modal window 'jitters' or 'shuffles' slightly after the transition has completed, as if it is kerning or loading a font.
Chrome 21 (stable for Ubuntu/Debian) much less smooth, quite jerky. The font 'jitter' isn't there.
Firefox 14. Smooth transition lasting about 1 second. The smoothness suggests more than 4fps. The text within the modal window 'jitters' or 'shuffles' slightly after the transition has completed, as if it is kerning or loading a font.
Chrome 21 (stable for Ubuntu/Debian) much less smooth, quite jerky. The font 'jitter' isn't there.