Cannot save Excel file exported to Firefox in Windows

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https://abrp.upvoty.com/b/report-a-bug/cannot-save-excel-file-exported-to-firefox-in-windows/
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This is a major bug! I edited a route for an upcoming trip from Florida to Colorado and can't save the Excel copy to my computer. I only get an error message that the filename cannot be found… Duh, it's a new file!