Fix double-tables in FF near responsive boundary

[nathanpbell]

FireFox calculates window width differently in media queries than it does in JavaScript. When responsive tables is viewed in FireFox at window widths near the responsive cut-off (ex: 768px), double tables can appear because the JavaScript has cloned the table in the HTML but the media query selectors haven't kicked in.

[dijichi]

chrome doesn't seem to like $.browser, and agents can be spoofed etc. it might be better to do something like this instead:
var FF = !(window.mozInnerScreenX == null);
if(FF) {
scrollBarWidth = window.innerWidth - jQuery("body").width();
}