Actually, that was just from just loading Gmail and letting it idle, a couple of weeks back, not actually using it. A year and a half ago, I recall it being more like 125MB, up towards 150MB as it was used. Gmail hasn’t really changed since then, but the Hangouts widget (which is pretty heavy!) might have, and the browser definitely has (I blame it for most of the increase). I haven’t actually used Gmail since around that time.

For reference, I’m using the explicit/window-objects/top(…) figure from about:memory. This is not an accurate representation of the full footprint, but is close enough.