DeltaWingDragon

If you don’t care about extensions, try some of those “DE default” browsers that never seem to be actual defaults. The ones like GNOME Web, Falkon, Konqueror, Midori (it was the default on one XFCE system once).

I would travel back in time and make Acorn RISC OS go mainstream. It’s a light OS with a full desktop environment, capable of playing video and rendering anti-aliased fonts, that boots all from ROM and runs on an 8MHz ARM CPU and 512 KB RAM. I said “go back in time” because I’m not sure how advanced it is compared to modern systems, it’s single-user only and has cooperative multitasking, instead of preemptive.