Firefox, show link URLs in status bar?

Going in the same order as above...

Show the URL over the Add-on Bar:

1. Using Stylish or userChrome.css, define the following CSS:

   statuspanel
   {
       z-index: 1 !important;
       bottom: 1px !important;
   }
   
   toolbar#addon-bar
   {
       z-index: 0 !important;
   }
   

   

With some extra tweaking, the final result can look like this (Windows 7):

label.statuspanel-label
{
    padding-top: 0 !important;
    padding-bottom: 0 !important;
    border: 0 !important;
    background-image: none !important;
    background-color: #cedaeb !important;
    color: #000000 !important;
}

Remove the delay and transition:

1. Set the browser.overlink-delay preference in about:config to 0. Restart Firefox.

2. Define the following CSS:

   statuspanel[type=overLink], statuspanel[inactive][previoustype=overLink]
   {
       -moz-transition: none !important;
   }
   

Allow URLs to span the whole width of the window:

1. Define the following CSS:

   statuspanel
   {
       max-width: 100% !important;
   }
   

Bonus:

If you are going to use the Add-on Bar as a permanent fixture, you can hide it's close button with:

toolbarbutton#addonbar-closebutton
{
    display: none !important;
}

Copy & Paste

Here is the combined CSS, sans Windows 7 theme:

statuspanel
{
    z-index: 1 !important;
    bottom: 1px !important;
    max-width: 100% !important;
}

toolbar#addon-bar
{
    z-index: 0 !important;
}

statuspanel[type=overLink], statuspanel[inactive][previoustype=overLink]
{
    -moz-transition: none !important;
}

toolbarbutton#addonbar-closebutton
{
    display: none !important;
}