I use my trackpad with touchegg and touchegg-gce for easier configuration. In the initial configuration there's an 'application' section for Chromium navigation which uses 2-finger drag that doesn't seem to work in Chromium or in Firefox (when I add Firefox).
The problem seems to be that the 2-finger drag is used for scrolling left and right. I have the feeling that an override for this function in Chromium or Firefox doesn't work and scrolling is "more important" than forward or back navigation.
With an iMac I saw that this is possible so did anyone get the trackpad to be usable for browser navigation?
You can emulate Firefox 'forward' and 'backward' navigation in Touchegg. The normal hotkeys that are used in Firefox for 'forward' and 'backward' navigation are alt-right and alt-left respectively, so it's just a case of configuring Touchegg with a sendkeys action to perform this. I use 3 finger left and right drag mapped to these hotkeys. This emulates the behaviour in Safari on a Macbook. Hope this helps.
I forgot to add that you also need to disable the Alt key from showing the Unity HUD otherwise you get a 'command' window pop up in the HUD when trying to navigate backwards and forwards. You can do this by running CompizConfigSettingsManager (CCSM), and then using the search filter for the 'Ubuntu Unity Plugin'. Next, disable the 'Key to show the HUD' (it's Alt by default, you can also map it to something else if desired).
After all this you should be able to navigate forwards and backwards in Firefox using 3 finger left and right swipes.
One thing you can check out, as well, is the about:config option in Firefox. Do a search on "swipe" and see if those are set to how you want.