Which functions do you want to perform with those gestures?

You can assign function to the related browser.gesture prefs on the about:config page.

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.

See "Gesture changes":

• https://developer.mozilla.org/en/Firefox_4_for_developers#Other_changes

These gestures automatically worked in firefox 3, pinching in and out on a mac track pad make things shrink and grow. The link says nothing about the gestures in question, and the value for these gestures in about:config is blank. Do you know what to put there? Or where i can find out where? Also, i was interested in the twist gesture among the settings, just thinking that would be great for tab switching.

found everything i needed here http://www.gottabemobile.com/2011/03/24/enable-pinch-and-twist-gestures-in-firefox-4/

Thank you to everyone that replied. I can now use the "pinch in and out" to shrink and grow. I went to http://www.gottabemobile.com/2011/03/24/enable-pinch-and-twist-gestures-in-firefox-4/ and then selected the Mac OSX Hints link. It was easy.