You can change the font to any font you want. Here is how,
1. Copy 'update_font_mod.v1' to root (SD card).
2. Copy your font to the 'Custom' folder (SD card).
3. Delete the original DroidSansFallback font in the 'Custom' folder.
4. Rename your font to DroidSansFallback.
5. Safely remove Kindle from your computer.
6. Go to Kindle Setting.
7. Press Menu one more time, you will see 'Update Kindle'.
8. Following screen instruction and wait for Kindle to re-boot itself.