Just bought a new Dell SK-8135 keyboard off of eBay.  I have one at work and like it a lot.

It has some buttons on it that are sort-of configurable — if you don’t mind poking around in the Windows Registry.

Start -> Run -> regedit

Browse to:  HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\AppKey

• 7 =  Browser home button – this will launch the default browser (which should be Firefox, BTW)
• 15 = Mail button  – this will launch the default mail app.
• 16 = Music note button – this will launch the application associated with the .cda extension.  I changed this one to .mp3, which is associated with iTunes.
• 17 = My Computer button
• 8 =  Calculator button

Make your changes, reboot and you’re good to go.