I have solved this issue by using the refresh feature.
Please note that it will revert Firefox to its original state: configurations and customizations, including extensions, extension data, and about:config preference configurations are removed.
Go the Troubleshooting Information page, that can be accessed by the following ways:
- Menu: Help > Troubleshooting Information.
about:support in your address bar.
Click the Refresh Firefox button.
For more information, visit: