Supports getting (and setting, when allowed by the spec) all the IDL attributes defined in the specification (value, max, position, labels), through ES5 getters and setters
Supoorts setting both max and value attributes, through mutation events
Will fix new progress elements as well, through mutation events
No extra HTML elements needed and none added through script
Browser support
The progress element is natively supported in: Firefox 6+, Opera 11+, Chrome, Safari 5.1
This polyfill adds almost full support in: Firefox 3.5-5, Opera 10.5-10.63, IE9-10
This polyfill adds partial support in: IE8
Supporting Safari 5 was impossible, as it completely drops the progress tags and gives you an error
How to use
Just add progress-polyfill.css in the head section and progress-polyfill.js near the body closing tag.