[OU] Customizing Opera -- how to map additional mouse buttons?

[Jordi Kroon]

I'm going over my mouse settings in Opera, and really want to map the  
"thumb button" on my mouse to Fast Forward. It now functions as 'back',  
which appears to be system default.

How can I address this button? I see references to Button5 and Button6,  
but nothing from Button4 to Button6 will allow me to change its action.

I have a Logitech G5, using Logitech SetPoint where this button is  
labelled '4', and set to 'Generic Button'.

I do not want to remap the mouse button everywhere, only inside Opera.

-- 
Using Opera's revolutionary e-mail client: http://www.opera.com/mail/