Time for a 20.04 LTS LiveCD memory comparison with a bunch more distros. I last did one in 2016.
Using Lubuntu as an example base memory usage approximately doubled from 2016 (251M) to 2020 (585M). Those numbers aren't strictly comparable because I'm not using the exact same setup as in 16.04 and I enabled more modern features (virtio graphics, EUFI, 4 cores).
Lubuntu is able to work with less at least partially because of Zram. The other distro that has Zram enabled is Endless, but they also use the Chromium browser which generally uses more memory than Firefox (also Elementary uses Ephipany). My guess is if Xubuntu enabled zram it's profile would more closely match Lubuntu.
Time limit for each applicaton launch is approximately 30 seconds.
Accuracy over 1G is by .25G increments. Under 1G, I tried to narrow it down to at least .1G.
Getting out of full screen on YouTube apparently is an intensive task. Dropped testing that.