Rated 5 out of 5 stars

A lightweight alternative to the bulky "Hide Caption Titlebar Plus". Together with "Firefox 4 UI Fixer" (for moving the statusbar and the menu button to reasonable places) it makes a compact elegant interface. The visual aspect can be improved by adding those lines to the userChrome.css file:
/* Change Title Bar color */
#titlebar-content {
background: #d4d0c8 !important;
}

/* Change title color and remove shadow */
#personal-titlebar tabs tab,
#personal-titlebar toolbarbutton,
#personal-titlebar toolbaritem > label,
#personal-titlebar menubar > menu {
text-shadow: none !important;
color: #000 !important;
}

This review is for a previous version of the add-on (1.0.20110330.1-signed.1-signed).