Hi,
I have noticed in recent versions of Chrome and Safari that the page will lock while it looks like Highslide is iterating over the DOM to find that elements to attach events to.
You can see in the Chrome timeline where the block is, is this the initial init
http://screencast.com/t/gUEyFui3fg
The DOM is large but not massive due to an CSS driven menu. FF doesn't seem to be affected as it doesn't "lock the page"
Try the following link in Chrome and then in FF and you will see:
http://tiny.cc/sdanc
Chrome gets 75% of the page rendered but not the images, runs the highslide script and then it releases
FF just goes straight through