element.style.cssFloat (styleFloat in IE) uses a convention of the browsers to assign attributes as property names in the html engine. Sometimes they work, other times not.
keywords can't be property names in a script- class, for, float become className, htmlFor, cssFloat or styleFloat.
The dom syntax is:
element.style.getPropertyValue('float'),
but that will only work for inline style assignments.
To get any stylesheet defined style you must look deeper:
document.defaultView.getComputedStyle(element,'').getPropertyValue('float');
Note- this is for firefox, opera, chrome, safari.
IE has its own methods for style look ups.