I've noticed that I get it frequently with Chrome, and not with the other browsers. I can only assume that this has something to do with the multi-process driven browser - remember that without any extensions, you have the "Chrome Web Browser" and the site you are visiting as two separate processes, and that could mean that the host recognises it as two immediate views as the same time - thus Forbidden.
All other browsers don't suffer from this from what I can tell.
Ahhh yeah, good point! but strangely in the past, chrome didn't used to have a problem here. it's been my browser of choice for a few years now though. it's only really the last few months where it has gradually been getting affected to the point where it is ruining my enjoyment of visiting this site. It hasn't impacted any other site I use, so it is just an annoyance to me really