By default the Back/Next gesture works with two fingers (in e.g. Safari) on the trackpad. Now it often happens to me when scrolling through iframes (with two fingers) I accidentally activate the back gesture. Now I changed it in settings to 3 fingers, but the animation is gone, and in Safari it's not anymore like dragging the page before from the left to center but like hitting the back-button (without animation)... Is it possible to use the real 2-fingers gesture with 3-fingers?
All you can have is to activate both the 2-finger and the 3-finger gestures. They work differently, though.
With two fingers you scroll the page to the sides revealing the page "below" it or the page "above" it according to the tag history.
With three fingers you just tell the browser to "go back" (swipe left) or "go forward" (swipe right) without any animation at all. At least this 3-finger gesture is consistent in many apps, including Finder.