I'm using Mozilla Firefox 6. Stack Overflow site continues loading infinitely. The spinner shows on the tab button and a message at the bottom "waiting for careers.stackoverflow.com". Why doesn't the loading finish?
OK, I think I found what's causing it - that's at least a start.
The main SO page contains three random job offers, for example:
Under the hood, the code that generates this is located here.
As you can see, it contains this part:
<img alt=\"\" class=\"impression\" src=\"http://careers.stackoverflow.com/ad/i/ibzx1oA-brrPe6s-hMAPzIA-12\" style=\"display:none\" />
That hidden image is most likely tracking beacon meant to track who is viewing what jobs, to prevent same jobs from being displayed again etc.. nothing wrong with that.
Now the question is: why your browser is blocking/choking on that URL? I couldn't reproduce the problem, with none of my browsers, including Firefox 8. I can only assume that one of your add-ons for Firefox is the culprit, try disabling the add-ons one by one until you find it.