Because sometimes, you just want to know what the browser is.
The good people over at JQuery decided that browser detection isn't the way to go. Their idea is that feature detection is the only way. So, $.browser was removed from JQuery 1.9 onwards. (Modernizr also doesn't support this).
Well, just peachy... I guess... Unless you want to provide a support page to clients telling them what they should already know - or one of the many other reasons you might want a quick way to see the browser type.
Quirks Mode came to the rescue with their own browser detection (http://www.quirksmode.org/js/detect.html). But alas, keeping it up to date was too hard. And so now recomments WhichBrowser (http://whichbrowser.net/)... but that seems to require PHP. Not ideal for everyone / every situation.
While I was personally updating Quirks Mode's old code, I stumbed upon this code included in an update from (mb)Menu (http://pupunzi.open-lab.com/mb-jquery-components/mb-_menu/). This adds in the missing $.browser back into JQuery.
As you would have read above, this is found in the (mb)Menu code. And I've not added any restrictions to it - so go nuts :) (Pupunzi uses MIT and GPL v2 for the licencing.)
Btw: Pupunzi is great. Have a look at www.pupunzi.com - some great stuff going on there. :)
I've updated this below to better handle the change in User Agent with the newer Opera browsers (which reports as OPR, not Opera)