The latest nightlies of upcoming Firefox 3.5 Beta 4 now feature a new option in the History menu to restore recently closed windows and not only individual tabs as in previous versions.

The new functionality should become a welcomed time saver those times we mistakenly close a handful of tabs, provided it is one of the last three windows closed, the current limit. You can change the number of “restorable windows” by updating browser.sessionstore.max_windows_undo to your preferred value via about:config.

Asked why wasn’t this feature implemented in a single menu option where a user can choose a window or a specific window tab, Mozilla Corporation’s Paul O’Shannesy, explains: “My primary reason is that windows and tabs serve a different purpose. By putting them in the same menu and giving them the same keyboard shortcut, I would argue you’re actually increasing memory load and forcing the use of the menu. If I were to close a window, then close a tab in a different window, I can’t get the window I closed back with a single key command. I have to click the menu, and look. By keeping the two separate, there might be one extra place to look, but they are clearly labeled. There’s an extra keystroke to learn, but it correlates to open window in the same way that undo close tab correlates with new tab.”

Firefox  3.5 Beta  is expected within the next couple of weeks and should be the last beta (despite nightly Shiretoko labeled as preBeta5) before entering release candidates and final version soon after.