Sadly (it happens to me too), most of these pages use either a Meta
<meta http-equiv=”refresh”>
or some form of Javascript to accomplish the reload every XX seconds.
For the former case, Firefox (not Safari) had an option to disable it (Tools >> Options >> Advanced >> General >> Accessibility -> Warn me when web sites try to redirect or reload the page).
However that option not always works, specially with newer sites; also that is a Firefox option only, which apparently you already knew about.
In the latter case (Javascript) there isn’t much we can do. As far as I understand, no CSS trick can prevent that (which would be the only tool we could have at the moment). I’m sure that at some clever (and bored) coder will create an extension that captures that and tries to prevent it.
In the meantime, you (and the rest of us) are out of luck while using Safari.
The ideal would be those sites to implement an AJAX form of communication that informs the user that there’s new content. All in all, it’s a series of hacks over a static protocol that maintains no “session” by design.