FEATURE REQUEST - show sum of memory and CPU of selected processes

Hi.

I was curious and wanted to see how much memory my firefox is using with hundreds of tabs open, but firefox uses a lot of separate processes and not just one, so there is no easy way to know how much in total it is using.

I though of two solutions: 1- the user can select with the mouse and shift or ctrl several processes and in the top or bottom of the cpu/memory columns the total is shown; 2- the user searches for something and only the processes that match that something show up in the list and in the top or bottom of the cpu/memory columns the total is shown.

Maybe there are better ideas.