Download the addon for Mozilla
Download the addon for Safari
Download the addon for Opera
How-to for chrome
- Download the .zip file and extract/unpack it.
- Open the options by clicking on the button next to the address bar.
- Click on "Settings" and then click on "Extensions"
- Tick the "Developer mode" checkbox.
- Click on "Load unpacked extension..."
- Select the directory with the addon files (from the unpacked .zip file). You should not delete this folder later.
- The addon is now installed.