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.

• /questions/777886

Thanks for the answer. It worked, but it was a bit of a pain. I'm sorry the new version of FF thought it was a good idea to remove this feature since so many Mac users have it.

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.