FileZilla is arguably the most popular FTP program in use today. It is safe, versatile and quick with easy user interface.
But you have to download it and run as a separate application. It is sometimes irritating to open another application, while surfing through your browser.
Now, firefox users can FTP files from their browser window itself. You just have to download FireFTP, a firefox addon, and install it. After installation, you can drag teh FireFTP icon to your toolbar. Whenever you need to do FTP, just click this icon, a separate tab will open, where you can transfer your files. You can choose to operate in Binary Mode, ASCII Mode or Automatic Mode.
The interface is very similar to FileZilla with easy drag and drop facility available.