On those somewhat rare (but not all that infrequent) occasions when Firefox locks up and hard crashes and all 6 or 7 of the windows that are open go up in a puff of virtual smoke, (each with their uniquely organized selections of tabs) - upon a restart of FF all of the windows return reliably. But when a clean shutdown of the program is initiated only the "top" window or two returns, and as far as I've seen there is a limited number to the "Recently Closed Windows" available to recover from the History menu. Clearly the state of the applications windows is preservable - why not recover all of them, similar to the "on startup pick up where I left off" setting for pages and tabs. (Incidentally Adobes applications exhibit similar behavior - the system actually works better and can recover the entire "workspace settings" but only if the power is abruptly cut off, (and no tedious waiting for updates to complete as a bonus!))