Sorry for the late reply. Please, open Control Pannel\Programs and Features and try to uninstall the 'Fiddler Syntax-Highlighting Addons' program.
If the solution above does not help, please, open the Registry Editor(you could type 'regedit' into the Windows' search box). Navigate to 'HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall' and delete the whole 'FiddlerSyntaxAddons' registry key.
Please, let me know if you face any other issues.
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