I finally managed to highlight the starting sphere after several tries. At first I wasn't sure if it was loaded.
Of course, I'm only using a 1.8 GHz Celeron with onboard GPU and 8GB Ram in Firefox, so... not exactly high-end stuff.
I know personally, anything 3d in Firefox is a slideshow, even with a 4090
It was laggy in Windows and under X11 on linux, but under Wayland I get 60-80fps and it's very usable.
Not sure what the cause is
EDIT: Under Chromium (compiled from AUR) the performance is roughly the same
For the dev, FF 117.0.1 on macos 13.4.
Firefox Developer (119.0b1), Chrome (117.0.5938.92), Opera (102.0.4880.56), Edge (117.0.2045.43).
Turning off all other programs (without crashing Windows), ranking for trying to drag the selection square ~2 inches x 2 inches (on a 1920 x 1080 laptop with the above noted characteristics) without doing anything else. Did the drag back and forth TL-BR, BL-TR 5-6 times to get a feel for general timing (cannot claim I used a stopwatch):
Edge: ~1 sec response before square changes
Chrome: ~1.5 sec response before square changes
Opera: ~1.5 sec response before square changes
Firefox: ~2 sec response before square changes
From my super low-end perspective, Edge is surprisingly responsive (maybe optimized for Windows?)
Edit: From another perspective, looking at the Dev Tools (what I actually care about), Edge is pretty hilarious, it has 72 errors on its default landing page (including this is not a "TrustedScriptURL"). Opera only has 2 "Uncaught (in promise)" and both Google and Firefox have 0.
There's something comforting about the idea that Microsoft still does not trust Microsoft. ("Left hand meet right hand. Begone fool, we have no hands!") The more things change...