Here is what I get when I tried the $ xev | grep button command:
Left button - state 0x10, button 1 same_screen YES state 0x100, button 1 same_screen YES
Right button - state 0x10, button 3 same_screen YES state 0x410, button 3 same_screen YES
Back button - state 0x10, button 2 same_screen YES state 0x210, button 2 same_screen YES
Forward Button - state 0x10, button 3 same_screen YES state 0x410, button 3 same_screen YES (AGAIN!)
Here is what I get when I tried the $ xev | grep button command:
state 0x100, button 1 same_screen YES
state 0x410, button 3 same_screen YES
state 0x210, button 2 same_screen YES
state 0x410, button 3 same_screen YES (AGAIN!)
Left button - state 0x10, button 1 same_screen YES
Right button - state 0x10, button 3 same_screen YES
Back button - state 0x10, button 2 same_screen YES
Forward Button - state 0x10, button 3 same_screen YES