[Ricky D'Angelo]

I don't know about fonts but if you are able to install google play on your tablet there are all kinds of alternative reader software available. I currently have Moon + Reader installed on my Fire tablet.
*edit*
Moon+Reader does allow for custom fonts (as well as change background). One difference from changing font on an kindle e-ink reader is that the fire tablet allows direct download of font to the tablet. On a regular kindle e-reader someone first has to download a font to a computer, then transfer it via usb cable to the kindle (in the right folder) which is ridiculous. Most kindles have an experimental browser so I don't see why a font can't be downloaded directly onto the ereader. It's a shame because perhaps an older generation of readers are missing out enjoying reading with different fonts due to lack of technical knowledge or lack of easy access to a computer. End of rant.

Below is a screen shot taken from my Kindle Fire (5th generation) with Google Play Store installed.