Firefox → Bookmarks menu → Manage Bookmarks → New Bookmark →
→ Bookmarks Toolbar Folder
That will create a bookmark that loads your del.icio.us inbox (or del.icio.us/popular if you prefer) in the sidebar, for easy browsing.
@-moz-document url-prefix(http://del.icio.us/inbox){
.right { display: none !important; }
}