Using scroll bar instead of wheel in chat history is choppy

I have a long history of chats and i was searching through it. I noticed that when i scroll using the bar (not scroll wheel) it was loading other things and hitching. Now thats fine but when i scroll up its still hitching. Its not only when loading another chunk of chats. I seems like its constantly unloading history and thats why its causing the hitching.

I am on Zen (Firefox based)