I can confirm that the question link does not react to mousing-over in Firefox 3.6.15 (Windows).
There seems to be absolutely nothing wrong with the HTML source for the link itself:
<h3><a href="/questions/178726/how-do-i-interpret-the-bellman-equation" class="question-hyperlink">How do I interpret the bellman equation?</a></h3>
Could you interpret this equation?
But something makes Firefox think the first line of the question excerpt is very tall. Here's a screenshot where I've selected the word "you":
So I suppose that when I'm mousing over the question link, Firefox thinks I'm really pointing at the question excerpt, where there's no hyperlink.
After some additional sleuthing:
Just before the U+3016 LEFT WHITE LENTICULAR BRACKET (that is, after the
(c_t,k_t)) there is an invisible U+2061 FUNCTION APPLICATION. The presence of U+2061 is what makes Firefox think the line extends far above and below the actual visible text.
This looks like a bug in Firefox, not one in the StackExchange server. But I suppose it wouldn't hurt if SE filtered out the "invisible operator" codepoints U+2061 to U+2064 that are now known to cause problems.
I have edited the question to remove the offending character.