Default values does not exist, except user_pref("browser.display.use_document_fonts", 0); Default -1
I made changes in Linux Firefox menu, then copied changes from configuration file Notebook to configuration file N800 opened in nano-tiny in ssh session. Using "standard" about:config is too complecate.

'GE Inspira' i replaced to 'Tahoma', which is more readeble on N800 screen.