Q: In Finder , why i can't go back and forward using the trackpad in Mountain Lion?

open System preferences >

Accessibility >

mouse and trackpad >

Trackpad Options >

Enable dragging "with Drag Lock" >

Done >

System preferences > Trackpad > choose: Swipe with two or three fingers.

close system preferences.

Now you drag lock with 1 finger, 3 fingers Swipe for Finder and apps, 2 fingers Swipe for web pages.

Hope this helps