From MozillaZine Knowledge Base
A keyboard shortcut is a key or set of keys that performs a predefined function. For example, pressing the "Ctrl+T" key combination (or "Cmd+T" on Mac OS X) will open a new Tab in Firefox.
For a list and description of keyboard shortcuts in Firefox and Mozilla Suite/SeaMonkey, go to the external links given below or look in the Help menu of your Mozilla application. For Thunderbird, see Keyboard shortcuts - Thunderbird.
Many keyboard shortcuts can be customized or disabled through the use of add-ons such as the Keyconfig extension or Menu Wizard. On Mac OS X, shortcuts for menu items can be changed from the System Preferences; however this may not work as expected due to bug 429824.