Starting with version 17, Firefox has a new set of preferences for mouse wheel actions. Unfortunately, this change makes it impossible to directly define "back in history" and "forward in history" actions for tilting the scroll wheel on tilt-wheel mice (something that used to be possible by setting mousewheel.horizscroll.withnokey.action=2 in about:config)
I use tilt-wheel mice almost exclusively and this is the only modern feature since the addition of the vertical scroll wheel on the middle button that I have been able to tolerate on mice. I just hate those new models that put buttons everywhere. But using the tilt-wheel for moving backwards and forwards in browser's history soon became second nature and now it's just annoying to be left without this feature.
Here's a quick workaround for this regression in Mozilla's software I found. Add the following to ~/.Xmodmap:
pointer = 1 2 3 4 5 8 9 0 0
This remaps pointer buttons 6 and 7 (horizontal scroll) to mouse buttons 8 and 9. Buttons 8 and 9 seem to be used by default in Firefox as shortcuts for back and forward buttons, so this solution doesn't require any additional poking around about:config. Of course, this also affects all other applications, so now you won't be able to use the tilt-wheel for horizontal scrolling.
Log-out and back in for the change to take effect or run xmodmap ~/.Xmodmap.
By the way, loading the .Xmodmap file in your home directory automatically when you log-in is not a given. GNOME display manager 3 on Debian seems to do it. Yours might not. If it doesn't work (you can check current button mappings with xmodmap -pp), check around /etc/X11/Xsession or /etc/gdm/Xsession.
Also, xmodmap seems to be deprecated in favor of setxkbmap, but I don't see any way of mapping pointer buttons with that.