Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
Try the steps below and check if it resolves the issue.
Disclaimer: If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk
Visit the link below for more information on registry back-up:
http://windows.microsoft.com/en-us/windows7/Back-up-the-registry
Click ‘Start’ and type ‘Run’ in the ‘Search programs and files’ box above ‘Start’ and hit ‘Enter’. In the Run window type ‘regedit’ (without quotes) and click ‘Ok’. Now navigate to the following location:
HKEY_CLASSES_ROOT\FirefoxURL\shell\open\ddeexec
At the right pane double click ‘(Default)’ and clear the ‘Value data:’ field and click ‘Ok’.