With Firefox Notify add-on, you can receive all Firefox notifications through Ubuntu's native d-bus notification system. Works for Gnome as well as KDE environments. It may work on other distros too, you have to try it yourself.
Edit: Also available in official Ubuntu repositories: sudo apt-get install xul-ext-notify
Search Ubuntu Packages
Lets you search Ubuntu packages right from Firefox search box.
This is really useful add-on for Ubuntu users. This add-on allows you to select shell commands from any web page and execute them just by a simple right click.
Install it (from the link below) and test it on following commands:
- df -h (show disk space)
- free -m (show Ram Usage)
This means that adding a ppa from any webpage is really simple :)
Download from here
You may also like: 2 Simple Chrome/Chromium Extensions for Ubuntu Users