I wanted such thing too (it is only one of very many things I would want in a new web browser program). I would also want to be able to save it to a file with a

I wanted such thing too (it is only one of very many things I would want in a new web browser program). I would also want to be able to save it to a file with a documented format, so that it can be examined, edited, copied, etc. Such a feature is then capable of doing other things too, such as a "duplicate tab" command, etc, which you can get almost "for free" when such a thing is implemented. (I also want the separate ability to save only form data to a file; sometimes saving the entire state is not wanted.)