Some gestures have been removed in Firefox 4 and later.

You can restore the zoom feature by changing the values of the related prefs on the about:config page.

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

To open the about:config page, type about:config in the location (address) bar and press the "Enter" key, just like you type the url of a website to open a website.
If you see a warning then you can confirm that you want to access that page.

• Use the Filter bar at to top of the about:config page to locate a preference more easily.
• Preferences that have been modified show as bold(user set).
• Preferences can be reset to the default or changed via the right-click context menu.

This FIX (See attached SCREENSHOT Image) seems to be working for most users: Type the following into the address bar: about:config

Then use the filter (top left side) and type the word, Gesture.

Make the following changes to the following 2 fields:

1. Numbered list itembrowser.gesture.pinch.in ~ enter the field and change the value to, itemcmd_fullZoomReduce
2. Numbered list itembrowser.gesture.pinch.out ~ enter the field and change the value to, cmd_fullZoomEnlarge

These changes should immediately restore the pinch gestures you are used to. Try it as soon as you make the changes and let us know. I've included a screenshot.

Note the changes in the 2 lines Hi-Lighted in Green and make them. This immediately worked for me. Good luck.

This did not work for me on Macbook Pro with FF6. Wish there was some help out there. Very frustrating.