an archived version of the page from the last time you visited it. If you haven't visited the page before or if you cleared the Firefox cache (see Chapter 14), Firefox displays an error message. Offline mode is useful when you won't have an Internet connection for an extended period of time and you want Firefox to use its archive instead of failing to load each page. For example, if you're preparing to go on a plane, you could visit a few pages, board the plane, put Firefox in Offline mode, and navigate among them as if you were still online. REMEMBER Putting Firefox in Offline mode doesn't actually turn off your Internet connection. It affects only the way Firefox displays Web sites. If you shut down Firefox in Offline mode, it will be in Offline mode next time you open it. To return to Online mode, choose the Work Offline command again. Exit Closes all open Firefox windows and tabs. Firefox displays a warning if any downloads are in progress and if any open windows contain multiple tabs.           The Edit Menu The Edit menu (shown in Figure A-3) lets you copy and paste text and images or find text in the current Web page. Figure A-3: The Edit menu. Undo Reverses the last text edit you made in the current window (such as in the Location Bar or a text box on the page). Note that Undo cannot reopen a tab after you close it, return a bookmark after you delete it from the Bookmarks Toolbar, or otherwise undo any action besides text editing. This command is unavailable (grayed out) when you haven't made any edits to undo. Shortcut Ctrl+Z ( +Z on a Mac) Redo Reverses the last Undo command. This is the opposite of Undo. If you type Firefox in the Location Bar and choose Undo, "Firefox" disappears. Choose Redo to restore it. As with Undo, Redo can only restore text edits. This command is unavailable (grayed out) when you haven't undone an action. Shortcuts Ctrl+Y or Ctrl+Shift+Z ( +Shift+Z on a Mac) Cut Copies the current selection into the system Clipboard and deletes it from its original location. Use the Paste command to put the selection in a new location. This command is unavailable (grayed out) when nothing is selected or when you have selected something that can't be cut out of its original location, such as text in a Web page. Shortcut Ctrl+X or Shift+Delete ( +X on a Mac) Copy Copies the current selection (which can contain both text and images) onto the system Clipboard, replacing whatever is currently on the Clipboard. You can then use the Paste command to put the selection in a new location. The difference between Copy and Cut is that Cut actually removes the text from a location, whereas Copy leaves the original and simply makes a copy of it. In both cases, the text that is cut or copied goes onto the Clipboard, and you can then paste it elsewhere. Although Cut doesn't work on text that is on a Web page, Copy usually does.