Here are some of our favorites:

• FireFTP is a free, secure, cross-platform FTP client for Mozilla Firefox which provides easy and intuitive access to FTP servers.
• 1-Click YouTube Video Download – Download YouTube in a single click. Download YouTube videos in FLV and MP4 (both High Definition and iPod compatible High-Quality)
• Delicious Bookmarks is the official Firefox add-on for Delicious, the world’s leading social bookmarking service (formerly del.icio.us). It integrates your bookmarks and tags with Firefox and keeps them in sync for easy, convenient access.
• Gmail Notifier – The original notifier for Gmail. Supports checking multiple accounts as well as Gmail Hosted accounts.
• LastPass Password Manager – Lastpass is a great password manager LastPass Password Manager is a terrific companion to this service.
• Omnibar – Integrates location bar and search bar into one. Shows search and url suggestions. Quickly switch search engine using search keywords. Provides different auto-complete popup styles for compact displays.