Ubuntu18.04 Browser Memory usage 64bit

Lenovo Thinkpad x230
Amd64
kernel: v4.20 & v5.0-rc6

opera  58.0.3135.47
firefox 65.0
chromium 71.0.3578.98

facebook.com
opera: 152 MB -170 MB
firefox: 231 MB -281 MB
chromium: 153 MB -186 MB

google.com
opera: 136 MB -161 MB
firefox: 210 MB -261 MB
chromium: 121 MB -171 MB

youtube.com
opera: 210 MB -266 MB
firefox: 285 MB -325 MB
chromium: 200 MB -258 MB