To use music symbol fonts other than its own integrated "Mozart Classic" font, Mozart (from version 10) requires (a) that the font is designed for use with Mozart (b) that it is installed in the normal way, and (c) the installation of a "mozart font description file" (.mzfont). These last are discussed here.
Mozart's Font Description Files have the unique extension .mzfont
Important: these are not fonts. They are only necessary or useful if you already have the appropriate font installed. Also they are not needed by Mozart 9 or earlier versions.
Font Decription Files must sit in the 'Data' folder within the Mozart program folder. It is sufficient just to copy them there.
This will depend on where you have installed Mozart but for English Windows systems the default location (for example for Mozart 10) will be C:\Program Files\Mozart10\Data\