When using Firefox in Linpus Linux (on an Acer One netbook) some hot keys don't work.
Ctrl + w
Alt + d
Ctrl + Tab
Does still work.
Edit: The version installed is 3.6.
You don't say what version of Firefox you have, but perhaps the Customizable Shortcuts add-on can help you discover the shortcuts that are enabled and change them if desired. You may want to consult the documentation on Keyboard shortcuts as well.
If that still doesn't help, is it possible you have another program running that is intercepting the hot-keys? Try disabling any browser add-ons or applications/system services that could be defining global hot-keys (Skype, Trillian, and display utilities are examples of possible culprits).