See usually I'd just use:
$.browser.webkit
Since we all know webkit is the only one which lets you style the scrollbar. However that's been removed in 1.9 in favour of:
$.support
Which is all fine and dandy except I'm pretty sure you can't check for scrollbar styling support this way. If you can, please let me know, or I'm just going to downgrade back to 1.8 again. The only reason I want to do this is because I'd rather use a built in system a browser has available rather than a javascript solution to style the scrollbar.