Tim J. wrote:
They should appear right under the pointer in a little pop-up box. If
the mouse is moving, the alternate text won't appear, so it must be
perfectly still.

I don't think there's a browser setting. Maybe it's pibkac. ;-) Is
anyone else having that problem?

You're expecting a non-standard feature to work the same in all browsers.
The alt attribute is not intended to be displayed in a popup when you hover
over an image. That's for text to display while an image loads or if the
user has image display disabled. What you're looking for is the 'title'
attribute. Here's the cross browser way to do what want:

IMG src="an_image.jpg" alt="some text" title="the same or other text"

--
Stan Gula
http://gula.org/roffswaps