How do I add favorite/specific sites to the Firefox 3.6 jump list?
From what I've read, the developers of a program have to implement jumplist features beyond the basics of opening the program and closing it. You might notice that Internet Explorer has the ability you're talking about.
I guess the team at Mozilla hasn't gotten around to that yet.
In the meantime, you can use Jumplist Extender to add your own things to a jumplist.
The only way I have found is to write an html file with contents like the following:
<html>
<head>
<title>Your Page Title</title>
<meta http-equiv="REFRESH" content="0;url=http://www.google.com"></HEAD>
<BODY>
</BODY>
</HTML>
Change to whatever site you want, and name it something like google.html then File->Open->Said file. Now it will be in the jump list as recent, which you can then pin.
A crappy work around but it works.