ajax calls work super fast on IE8 and not sow fast 1~ 0.5 sec on other browsers

Question

I have something like a blog where user adds a new post the new post is shown together with the others (all the requests to the server are using $.post)

on IE8 everything works super (A robot would have the possibility to add 10 posts a second) but on other browser the time until the new post appears is 0.5 ~ 1 sec

anybody knows why ?
how to make it fast on other browsers ?