Ack -- no, the mouseover text works in IE, but I've never managed to get it to work in Firefox. There's a way you can view it in the code, though:

Hit Control + U to open a window showing the HTML source coding.
Scroll down till you spot the date on the left side. (12:00 7th May, for example)
Skip the block beginning 'td valign="top"
Look at the block beginning 'a href="http://pics.livejournal.com ' etc.
Scroll right to follow that line, and you should see the alt text.