Got this info from http://support.mozilla.org/en-US/questions/795269, and cor-el helped on it.

Below is the copy of the information from above:

• browser.gesture.pinch.in -> cmd_fullZoomReduce
• browser.gesture.pinch.in.shift -> cmd_fullZoomReset
• browser.gesture.pinch.out -> cmd_fullZoomEnlarge
• browser.gesture.pinch.out.shift -> cmd_fullZoomReset
• browser.gesture.pinch.latched -> false

And, it works!