I also have the MX Duo, and had some problems browsing with my mouse. I was having problems using the middle mouse button with Firefox AND
IE. I ended up just uninstalling the stupid MouseWare software and everything works fine now. I would try uninstalling it and seeing if it works. The MouseWare isn't all that great anyways.
As far as using the keyboard features with Firefox, same goes for me also...
Hopefully Logitech fixes this with updates on the software used or someone can tell us what to do.