On a new install of ubuntu 10.10 (you do not say which version of linux you are running), accessed via vnc (the only way to get to a GUI on that laptop), every time I pressed lower case "d" in a firefox address bar, the stupid thing minimised all my windows.
The solution for me was to mouse to System - Preferences - Keyboard shortcuts.
Then find the "d / D" shortcut, and disable it (it was set to minimise all windows).
What took me time to work out is that you have to logout and back in again for this to take effect (or in my case restart the vnc server). Is ubuntu broken? Probably.
Hope this helps.