demonstrates that Firefox is somehow using an ungodly 13.6 GiB of memory, the detailed process breakdown reports that it’s using merely 600 MiB despite one of its immediate child processes using 1.3 GiB!
You misunderstand the numbers.
The application (picture 1) shows the total amount of memory everything around firefox consumes.
In the second picture, firefox is the shown as the process firefox, and below all the other stuff connected to firefox and how much memory they consume.
If you take the memory consumed by firefox on the second picture, then add together ALL the suff below in that tree, you will end up with the number shown in picture 1. Or at least you should… xD
Edit
Also, dont forget that one gibibyte (GiB) is 1024 mebibytes (MiB), not 1000.
@bedna, so although the child processes might add to 13 GiB, the process tree view displays solely the memory being used by that that process, excluding its children?
Yeah, don’t worry — since the SI and IETF have finally got their act together, formally separating the base-10 and base-2 measurement systems, it’s actually the system taught in schools now (albeit inconsistently, as expected) so I’ve been using both my whole life.