Macbook Air OS X 10.8.4 Trackpad Pinch Zoom not working in Firefox 23.0.1
You can restore the zoom feature by changing the values of the related prefs on the about:config page.

browser.gesture.pinch.in -&gt; cmd_fullZoomReduce
browser.gesture.pinch.in.shift -&gt; cmd_fullZoomReset
browser.gesture.pinch.out -&gt; cmd_fullZoomEnlarge
browser.gesture.pinch.out.shift -&gt; cmd_fullZoomReset
browser.gesture.pinch.latched -&gt; false