FRX with 500 comments loads ~40 seconds

FRX content size is 4.7MB which transfers for 24.79s and 20.03s server spends on its generating. Slow instance + slow Internet connection - the main reason why there is such a big delay.
This can be fixed by rewriting the way FRX renders - there is no need to render all comments on server side and send them to the client.

The issue found in 3.9.0, but seems like it's an old one.