It seem's that Firefox intalled by default with Lubuntu 13.10 is not localized (in french for my case). I performed a clean install ( booting live on Usb key, and then installing, using french language,and choosed not to keep anything on hard disk ) I have "FR" on systray, and on synaptic, I can see that "firefox-locale-fr" is installed ( but "firefox-locale-en" is installed too. Any clue to get firefox in french ?