[jQuery] css() function returns different results on different browsers

[upsilon]

Hi everyone!

Today I've tried to create simple hover effect on a <div>: if the
cursor is over the box, the background-image css property of the div
is modified.

On the HTML side, a <div> with an id:
<div id="round"><p>Blah blah</p></div>

On the CSS:
div#round {
background-image: url(pics/bg_round.png);
}

In order to get the background-image property, I wrote:
var imgName = $("#round").css('background-image');

The issue is on what I get from this function in Internet Explorer and
in Firefox:
IE : url("http://blabla/images/bg_round.png";)
FF : url(http://blabla/images/bg_round.png)

OK, the difference is not huge, and I've already solved the problem by
replacing quotes by nothing in the string.

But... Is this a bug? A feature? jQuery is intended for erasing
differences between browsers, and here it's not the case...
What do you think of it?

Thanks!
upsilon

PS: sorry for my English (I'm French), I'm afraid that 15 years of
studies aren't enough for me... :(