My current userChrome.css changes for customizing the Firefox interface. Utilize the ChromEdit extension above for easy profile editing.

/* ---------------------------------- [ toolbars ] -- */
/* Remove spacing between menu items on toolbar */
menu {padding: 2px !important;}
/* Toolbars without borders */
menubar, toolbox, toolbar {
border-style: none !important;
}

/* -------------------- [ margins & padding ] ------ */
/*allows increase or decrease of padding or margin around icons selected for bookmarks */
#personal-bookmarks toolbarbutton {
margin: 0px 2px 0px 2px !important;
padding: 0px 0px 0px 0px !important
}

/* Remove extra padding from the Navigation Bar */
.toolbarbutton-1, .toolbarbutton-menubutton-button {
   padding: 0px 0px 0px 0px !important;
margin: 0px 0px 0px 0px !important;
}

 .toolbarbutton-1[checked="true"], .toolbarbutton-1[open="true"],
.toolbarbutton-menubutton-button[checked="true"],
.toolbarbutton-menubutton-button[open="true"] {
   padding: 0px 0px 0px 0px !important;
margin: 0px 0px 0px 0px !important:
}

/* ------------------------------ [ menus ] ----------- */
/* Remove the Go and Help menus
   (These are just examples. Try changing "Go" to "Edit" or "Bookmarks") */
menu[label="Go"],
menu[label="Help"],
menu[label="Edit"]{
   display: none !important;
}

/* Remove read mail from Tools */
menuitem[label="List of Tabs"],
menuitem[command="Browser:ReadMail"],
menuitem[label="New Message..."],
menuitem[label="JavaScript Console"],
menuitem[label="Page Info"]{
display: none !important;
}

/* --------------------------------- [ misc ] -------------- */
/* Removes majority of menu separators */
 menuseparator {
display: none;
}

/* Make the Search box flex wider */
#search-container, #searchbar {
  width: 236px !important; }

/* Cosmetic effects to line everything up */
.tabs-closebutton {
   padding: 1px !important; }

/* -------------------- [ contextual menu items ------ */
#context-back,
#context-forward,
#context-reload,
#context-stop,
#context-viewsource,
#context-openlink,
#context-viewpartialsource-selection,
#context-selectall,
menuitem[label="Reload Tab"],
menuitem[label="Reload All Tabs"],
menuitem[label="Close Tab"] { display: none !important; }

menuitem[label="Open"],
menuitem[label="Expand"],
menuitem[label="Manage Folder"],
menuitem[label="New Folder..."],
menuitem[label="Show Only This Frame"],
menuitem[label="Open in New Window"],
menuitem[label="JavaScript Console"],
menuitem[label="Reload Frame"],
menuitem[label="Bookmark This Frame..."],
menuitem[label="Save Frame As..."],
menuitem[label="View Frame Source"],
menuitem[label="View Frame Info"],
menuitem[label="Open Frame in New Window"] { display: none; }

In order to convert older Firefox extensions to play nice with Firefox 1.5 , follow the steps below:

1. Save the extension (.xpi file) to your desktop. Open the .xpi file with an archive utility like WinRAR or WinZIP.
2. Open install.rdf and change 1.0 to 1.6 then save the file.
3. Drag the .xpi file into an open Firefox window to install.