Looks like I am not alone to have noticed this slowdown.
See https://community.windy.com/topic/37571/windy-web-site-is-quite-slow

I checked with Safari (version 13): no slowdown at all.

Looks like I am not alone to have noticed this slowdown.
See https://community.windy.com/topic/37571/windy-web-site-is-quite-slow

Sorry for the late answer.
My mac is 14 years old.
OS : High Sierra
Firefox: 115.17.0 Firefox ESR (latest available)

Additional info: on the following web site, https://www.vendeeglobe.org/cartographie, I don't have this issue: Panning and zooming are very smooth

For about a month or two, Windy web site has become slow on my old Mac : panning and zooming is now slow (lag). Particles look also slower.
I am on Firefox. More or less the same problem with Safari
No problem with other web sites