I got the answer for you
The code that Neopets use does not follow the W3C standard, alt="Here's that bubble" is not the correct way to display that bubble, alt= is to be used as an alternate text description for an image, if that image fails to appear, of for blind people who get's sites read for them, they can not see the image so they get the alt="text" read for them.
The right way is title="Here's that bubble" but I guess neopets doesn't use that.
Browsers like IE etc that does show alt= as a bubble is doing things wrong and doesn't follow the official web standards. Mail the neopet crew and ask them to add the title= (Or better yet, exchange alt to title where alt shouldn't be used) as IE and the other browsers understand title= as well.
Ehm, you that doesn't get what I'm babbling about: this is the code for an image in XHTML/HTML
<img src="the image.gif" alt="text to show if the image is not available, broken etc" title="This is the Image!"/>
Neopets left out the title= and used their tool tip popup in alt= instead, which is wrong
The alt should still be there though, for the blind etc etc.
More about it here:
http://www.w3schools.com/tags/tag_img.asp
and here:
http://www.w3schools.com/tags/standardattributes.asp
"alt: Defines a short description of the image"
"title: A text to display in a tool tip"
Everything comes down to that Firefox is much more strict with following standards than IE. Which is a good thing, the error is in the code, not in Firefox.
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<silja rox my sox>... somewhat