I assume that you see a green block and not a checkmark in the folder properties as that used to behave like that in older Windows versions. Windows shows a green block for folders in the Read-only box, but not a real check-mark. Only a check mark in the Read-only box means that a folder or file is Read-only. Windows doesn't check all the files in a folder so instead displays a green block to indicate that it is not sure. You can look at each file individually to see if any are read-only. Easiest to do that is to make the Attributes visible in "View > Details" mode: Choose Details in Windows Explorer. ---- Try to start Firefox in <u>[[Safe Mode|Safe Mode]]</u> by holding down the Shift (Mac: Options) key to see if that helps. Create a new profile as a test to check if your current profile is causing the problem. See "Creating a profile": *https://support.mozilla.org/kb/profile-manager-create-and-remove-firefox-profiles *http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Profile_issues If the new profile works then you can transfer files from a previously used profile to the new profile, but be cautious not to copy corrupted files to avoid carrying over problems. *http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox Boot the computer in Windows Safe mode with network support (press F8 on the boot screen) to see if that has effect. *http://www.bleepingcomputer.com/tutorials/how-to-start-windows-in-safe-mode/ *http://www.7tutorials.com/4-ways-boot-safe-mode-windows-10

Successfully created a new profile and got Firefox to start. Shut Firefox down to install and add on and now get the same message again.

Is the profiles.ini file created or updated properly to show the location of the profile? *http://kb.mozillazine.org/profiles.ini_file What error message do you get (if any) when you try to start Firefox?

The ini file was pointing to corrupt Profile. Seems to be working now.