“Original weight” doesn’t match developer tools

[eeeps]

Page in question:
http://ericportis.com/etc/demo/status-quo.html

Sizer Soze reports that it weighs 5.45MB.

Chrome and Safari think it weighs ~3.5MB.

Firefox consistently thinks the images weigh 1.333x the size reported in Safari and Chrome (?) and measures the page at ~4.8 MB. But its dev tools sizes don't match the content-length HTTP response header, so I'm considering this a Firefox bug?

I just want Sizer Soze to match something, or understand why it doesn’t.

Detailed per-resource breakdown:
http://ericportis.com/etc/resource-size-differences.html