Hello!
Long time Firefox user here.
I use a custom monospace font from the Advanced font options:
I would love to see more options to customize fonts in Orion! It will allow users to use a set of fonts of their choice (not just one) to display. I also note the checkbox "Allow pages to choose their own fonts, instead of your selections above" which is quite interesting to give more choices to the users.
I am using Orion Version 0.99.126.4.1.7-rc (WebKit 619.1.1), here is the only font customization option I found under "Appearance":
As shown in the previous paragraph, in Firefox these fonts options are "Advanced", I think it is a good idea to not bloat the Appearance settings with that.