I have two buttons on my mouse to go forwards and back:

They used to work all right in Firefox, but now they don't any more. I've since switched to Google Chrome (the package from google.com/chrome, not chromium).
I haven't changed any configuration to do with input devices in the mean time.
xevdoesn't seem to recognize the buttons. The others work well. Even the weird zoom-slider on this mouse is recognized by xev. It's only the forwards and back buttons that don't do anything.
How do I get them to work?
The mouse is a Logitech VX Revolution in case that's important.
Edit at Dec. 10th, 11pm:
The back button has just started working, after an update. I'm confused. :P
The forwards button still doesn't work. xev recognizes the back button now, not the other one.
