Try completely removing Firefox one more time as follows: (from http://smallbusiness...efox-80256.html )
How to Totally Remove Firefox
by Andrew Meer
By default, the Firefox Uninstall Wizard does not remove your Firefox installation in its entirety from your hard drive, leaving behind user data, such as bookmarks and passwords intact. While you can instruct the Firefox Uninstall Wizard to remove your user data during removal, you must still manually delete any remaining files that are left behind, such as the Firefox installation folder and browser cache.
Removing Personal Data
When uninstalling Firefox using the Firefox Uninstall Wizard, check the box next to “Remove My Firefox Personal Data and Customizations” to remove all user data. If you already uninstalled Firefox without removing your user data, press “Windows-R” to open Run, enter “%appdata%” (without quotes) and then press “Enter.” On the File Explorer window that shows up, select the folder labeled “Mozilla” and then press “Shift-Delete” to remove all user data manually.
Removing Additional Files
The Firefox Uninstall Wizard leaves behind the folder that Firefox was installed to, which may contain remnants of data related to installed add-ons. To remove this folder, open File Explorer and navigate to “C:\Program files,” or “C:\Program files (x86)” on 64-bit versions of Windows. Select the folder labelled “Mozilla Firefox” and then press “Shift-Delete” to remove it. Since the Firefox Uninstall Wizard also leaves intact the folder that stores any cached Internet files, open Run, type “appdata” (without quotes) and then press “Enter.” Double-click the folder labeled “Local,” and then select “Mozilla.” Press “Shift-Delete” to remove it.
Reboot, then download and install the latest Firefox, see what happens.
Edited by Ztruker, 21 November 2017 - 08:38 PM.