15Mb when measured through about:performance 70Mb when measured through about:memory

I don't know why they are different.

17.35 MB for me in Firefox 76.0.1 on MacOS 10.15.4.

But it has been a couple hours since your comment and the other replies :)

I have 10.4 MB on firefox and, on Chrome is 33 MB.

I get 11.1 MB in Firefox.