Add to Favorite FF2

On our site we have an add to favorites link that only displays in IE - because it doesnt work in other browsers.
The idea being that if it wont work then you wont see the link.
The code says
if(window.external)
{
//write the link
}

But in FF2 the window.external condition is returning true but window.external.AddFavorite is not a function (it says)

how can we make this work in FF2?

On our site we have an add to favorites link that only displays in IE - because it doesnt work in other browsers.
The idea being that if it wont work then you wont see the link.
The code says
if(window.external)
{
//write the link
}

But in FF2 the window.external condition is returning true but window.external.AddFavorite is not a function (it says)

how can we make this work in FF2?
if( window.external && typeof window.external.addFavorite != 'undefined' )
window.external.addFavorite(...,...);

works perfectly, cheers