The automatic reload is probably done with a script. You could try the NoScript addon and then enable or disable scripts until you find the offending one. It might stop the site working properly, though.

You can do the same with AdBlock Plus - block scripts one by one.

The site use a meta refresh tag: <meta http-equiv="refresh" content="900;url=http://www.pajamasmedia.com/instapundit/"> You can look at: Refresh Blocker: https://addons.mozilla.org/firefox/addon/992

cor-el's reply is close since the problem site apparently does use a meta refresh tag. But it's only half the answer since the Mozilla addon "Refresh blocker" notifies me when it functions. I need a process that disallows the reload but doesn't need to let me know about it - that is one that doesn't print stuff such as:

RefreshBlocker: http://www.pajamasmedia.com/instapundit/ Timeout: 900

I have the same problem, but I use a Mac, and I have this issue with Instapundit regardless of which browser I use. Very frustrating, as it's one of my favorite blogs.