I guess you're not going to be able to see the font because of the mapper.
It's normal for some games to switch CHR-ROM midframe. In that case, you'd just adjust the PPU/Nametable Viewer in FCEUX to display on any scanline where text is displayed.
But it looks like MMC4 is a special case (used only on Fire Emblem/Gaiden, Famicom Wars, and maybe Japanese Punch-Out). It allows them to use special tiles (FD and FE) to do CHR-ROM swaps mid-scanline. Unfortunately, FCEUX's viewers won't let you choose the horizontal position where the viewer windows are refreshed.
(meaning that whenever the PPU tries to draw the special tile numbers, it'll do a bankswap instead)
So, you're out of luck being able to view the font in this game.
