Basically the same thing. It's been several hours, right now it says it has 644 MB of explicit allocations, it is 675 MB resident, and has 1,633 MB of virtual address space. When I looked at about:memory right after composing my original post, the numbers were within a few megabytes of what htop reported.

Putting that in Chrome gets me to a page that was new to me, chrome://memory-redirect/

I never knew this existed...thanks for pointing this out.