Winifred, Thank you for your question, please try the following to start Firefox: *[[Troubleshoot Firefox issues using Safe Mode]] Shift+click Firefox to start Firefox in Safe Mode. If the error still appears its a corrupt extension. *[[Back up and restore information in Firefox profiles]] *Then start Firefox with Profile Manager: [[Use the Profile Manager to create and remove Firefox profiles]] and create a new profile. If creating a new profile gives an error, consider removing the extension folder in the profile or making a back up of the profile and reinstalling.