Install IDM Firefox add-on (IDM CC) for Firefox 13

• Get the latest Firefox 13 from here
• Extract it and install.
• Get IDM CC 7.3.18 Firefox add-on from here
• Extract the file. It contains a .XPI file.
• Open Add-ons page of your Firefox 13 browser.
• Click on the gear icon (left to the search box).
• Click on Install add-on from file... menu item.

• Now choose the .XPI file that you just extracted from the .7z file you downloaded above.
• Install the Add-on.

• Congratz! You've installed IDM CC for Firefox 13.
• Now restart your browser and enjoy!