The font depends -- like all fonts inside applications -- on the setting in System > Preferences > Appearances. There on the tab Fonts the "application font". Changing this for gwibber would be inconsistent and break the design of the desktop.
The font depends -- like all fonts inside applications -- on the setting in System > Preferences > Appearances. There on the tab Fonts the "application font". Changing this for gwibber would be inconsistent and break the design of the desktop.