Here’s a great talk to get you up to speed! https://youtu.be/y1MCLZm8yAY

It's not very responsive

From memory when I worked there 10 years ago, all the Javascript based stuff was pretty slow in a very noticeable way. They've likely gotten better as they are using a well known Javascript and rendering engine, so they're getting many optimizations for free.

They're very involved in web standards. Rob Palmer from Bloomberg is co-chair of TC39.