I cannot open Firefox as I get the message that Firefox failed to read configuration file. I uninstalled and reinstalled latest version and still cannot open with the same error.
Last week when the automated upgrade came I said yes and then stopped it midway as it was not a good time to reboot my laptop. Since then, when I try to open it says cannot read configuration file - even when I uninstall and reinstall - still cannot open it with the same error.
Uninstall your current Firefox version and remove the Firefox program folder before installing that copy of the Firefox installer.
Do not remove personal data if you uninstall the current version.
It is important to delete the Firefox program folder to remove all the files and make sure that there are no problems with files that were leftover after uninstalling.
Your bookmarks and other profile data are stored elsewhere (not in the Firefox program folder) and won't be affected by a reinstall, but make sure that you do not select to remove personal data if you uninstall Firefox.