This is feedback. You press a shortcut; how do you know it worked or not? You do because the corresponding menu rapidly blinked. Or you double click an icon and suddenly a rectangle appears in another part of the screen. Is this related? Here the animation shows that yes, the icon transformed into a window.
On the other hand on my mobile Firefox I wait seemingly a half second each time I long press a link, because there is an animation that zooms a context menu. It does not zoom from the link, which could be justified maybe, but always in the same place in the center of the screen. This animation is meaningless and thus wasteful.
On the other hand on my mobile Firefox I wait seemingly a half second each time I long press a link, because there is an animation that zooms a context menu. It does not zoom from the link, which could be justified maybe, but always in the same place in the center of the screen. This animation is meaningless and thus wasteful.