The Fontself Maker extension currently exports fonts as OpenType files (.OTF) but you can convert this .otf file to TrueType (.TTF) or webfont formats like Web Open Font Format (.WOFF), WOFF2, .EOT or .SVG with other tools if needed.

You can try using: http://www.fontsquirrel.com/tools/webfont-generator

To generate a TTF file, just click on Expert... & select TrueType in Font Formats.

Now may we just ask why you specifically need TTF? ;)

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