If your jquery.corner.js is not working with firefox 4 then a small modification of your plugin can make it OK for firefox 4.
Open your jquery.corner.js file. At the beginning of the code you will find some code like
var style = document.createElement('div').style; var moz = style['MozBorderRadius'] !== undefined; var webkit = style['WebkitBorderRadius'] !== undefined; var radius = style['BorderRadius'] !== undefined;
In this plugin,
var moz = style['MozBorderRadius'] !== undefined;
was actually for firefox. But from firefox 4 there is no longer exists -moz-radius, that means style[‘MozBorderRadius’] will not work for firemox 4 anymore.
For firefox 4, they use the standard “border-radius” for curve corner of an element. So change the line
var radius = style['BorderRadius'] !== undefined;
var radius = (style['BorderRadius'] || style['borderRadius']) !== undefined;
This change of jquery.corner.js plugin will work for both old firefox version as well as Firefox 4.