Hyperlink to javascript function doesn't work in Firefox

Strange.  This hyperlink works fine in IE7 and in Safari but it doesn't fire the javascript function in Firefox (...which leads me to believe it may not work in IE8, either). 
<asp:HyperLink
ID="hlMostPopularPrint"
runat="server"
NavigateUrl="javascript:ShowLists('prints');">
Most popular print images
</asp:HyperLink>
Any ideas why and how to fix it?

Thanks,

John
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