If JS had a decent regex engine, you'd just use a lookbehind instead (?<=^|;) but it doesn't so that wont work.

Next best solution is probably splitting and looping:

FoliosecCookie = getCookie('foliosec');

function getCookie( Name )
{
	for ( CurCookie in document.cookie.split(';') )
	{
	    var KeyValue = CurCookie.split('=',2);
	    if ( KeyValue[0] == Name )
	       return KeyValue[1];
	}
	return '';
}

You may need to use decodeURIComponent on the return value.

And for anyone wondering why the browsers don't just provide a built-in getCookie method that accepts a name and returns the value, the answer is because browser developers are fucking stupid.

/; foliosec=[a-z]+;/

And it really isn't voodoo; it's a very easy language to learn.