How to know each TAB memory usage ?

In Firefox Quantum, you can use about:performance.

There is also about:memory where you can "view, save, load, and diff detailed measurements of Firefox's memory usage".

Answer history:

EDIT 1

An user requested this feature five months ago in Mozilla Support forum. Quoting the answer of the moderator, "Mozilla is working on that through the Electrolysis project".

EDIT 2

Project Electrolysis has been released! Now Firefox is also multi-process.

For Firefox, I've made an addon which displays tab memory usage in the corresponding tab's title.

Provides user with tab related stats and memory usage ..

https://addons.mozilla.org/firefox/addon/tab-data/

Features

• How many tabs are currently open
• How many tabs have been opened during this Firefox session
• How many tabs have been opened since addon installed
• Display tab memory usage in title
• Preference to toggle tab memory usage on/off
• Preference to set interval between memory usage collection