Icecat is a GTK3 application. Have you tried setting your GTK3 font? You can do so with an application like lxappearance (under the "widget" tab, select "Default font")
Alternatively you can set it manually. If I'm not mistaken it should be in the file: ~/.config/gtk-3.0/settings.ini At the bare minimum I think you should have this: [Settings] gtk-font-name=<My Font> <Weight> <Size> The weight can be things like "Regular", "Medium", or "Bold" or other variants Make sure your font is being located correctly by fontconfig. You can test it with: fc-match "My Font" Also, for the record you might want to check what gets returned when you just type fc-match with no options. Because that's usually the default most applications will select, and it sounds like you might have it set to a monospace font, which probably isn't the best setting in general.
