On a Mac. Both Chrome and Firefox invariably over a day of browsing accumulate oodles of memory and must be quit and reopened. Closing every window hilariously leaves this situation:
https://i.imgur.com/jZNoC0I.png
Zero windows, 3.5GB of memory used. Sitting around, it's not as if that memory gets cleaned up.
The frustrating part is trying to be "good" and not have hundreds of tabs open at any point doesn't seem to help -- the memory still piles up, eventually driving the responsiveness of the entire system into the shitter.