Please add a new feature that allows the user to manage windows of open tabs in a collective, subject-based manner. Add a new menu to File, "Save Window As...", under "Save Page As...". menu. The feature would allow us to name and save an entire window of tabs organized for a particular subject. Later, we could open a named window, update the tabs, than save and close it again for future use. Being able to save, close, and reopen later a tabbed widow will significantly reduce the impact that FF has on computer's resources.
I normally have 1 to 2 dozen windows open, all the time, each with a few to many tabs. As such, it get's difficult to manage them all, difficult to find the one that has a ta you're looking for, etc. Managing each window independently, having opened only the ones that are currently needed, would really simplify browsing.