- Copied FirefoxPortable.ini from Other\Source to the folder containing FirefoxPortable.exe and made sure all the entries in it were correct.
- Tried to run "FirefoxPortable.exe -p" but found out later that it was not portable.
- Made an %appdata%\Mozilla\Firefox\profile.ini file and a Profiles subfolder (both empty) under that folder.
- Did not tamper with the App folder, except for deleting Firefox64.
Nothing worked. This seems to be a new problem as I couldn't find any solution on the Web.