dimensions plugin Mozilla bug

While playing with Ext I encountered a problem in Firefox whereby the offset function in dimensions was causing an elem.style error. The reason is that there is a do-while loop if options.scroll is set, and that loop will go all the way up to the document, at which point - if the browser is Mozilla - the code attempts to check the css for overflow not visible and falls over because document has no style.
I fixed this in my version by modifying line 260 of dimensions.js and inserting a check for op, so the line now begins ...

if (op && jQuery.browser.mozilla && ....

This prevents the jQuery.css() call failing at the document level.