What was that tab you closed about three tabs back again? Could it have been the fourth tab back, before you got your coffee? If you find yourself using the Ctrl + Shift + T keyboard combination to bring up lost tabs a lot, there is a better way to get the job done. The Undo Closed Tabs Button add-on for Firefox gives you a few ways to save your lost tabs.
This extension allows you to undo closed tabs via a toolbar and/or tab bar button or the right-click context menu. Also it comes with a much easier keyboard combination of its own to remember, Ctrl + Shift + Z. You must add the toolbar button by going to View -> Toolbars -> Customize, then drag and drop the icon where you want it on the toolbar.
Save your lost tabs, and save yourself a lot of wear and tear on your Ctrl and Shift keys while you are at it. Your keyboard will thank you!