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.