When you update your Firefox version IDM CC requires an add-on may also need to update. Not difficult to perform the update, follow my instruction..
Update IDM
Please update your IDM software. This is simply the new version of IDM will have further improved the old version. Please turn on IMD and click "Help" and click "Check for update..".
Appears a small popup checking for new version

If there is a newer version IDM version you are using, it will display a popup with information about it. Please click Update Now.
The update steps you easily done, so I do not guide.
Update IDM CC
If you do not want to upgrade the new version, please upgrade IDM extension IDM CC 7.3.91.First you access url: http://www.internetdownloadmanager.com/support/firefox_integration.html
Scroll down the page and click the Install button

File IDM CC has been downloaded

You click on the gear icon and click "Install Add-on From File..."
You choose the IDM CC downloaded file to install. Then you enable IDM CC and restart Firefox. Now everything is ready to work!
When an error occurs, you need to upgrade the software IDM or just upgrade utility IDM CC. Internet Download Manage the most popular programs available today. Many hackers have taken advantage of this to create a crack that contains malicious code. Consider downloading the software and virus scans periodically remember to protect your computer.