Given Firefox 18, when I use "File" -> "Close Window" (or hit Ctrl+Shift+W) with another browser window open and multiple tabs in the current window, I am asked "You are about to close [some number of] tabs". However, when I do the same thing in the last open Firefox window, it asks me if I want to quit and whether to save the tabs for the next invocation, without specifying how many tabs I have open in that window.
Often, I want to get a quick count of the number of tabs open, and aborting closing the window is a quick way to get that number. But as it is, if I have only one browser window open, I need to open another browser window simply to get the question I want.
Can Firefox be configured to display the count of the number of tabs also when closing the last browser window of the running instance? How?