Ubuntu may come with a lot of dictionaries installed, so you may have to uninstall dictionaries that you do not use/need. You can check these locations for globally installed dictionaries: */usr/share/hunspell/ */usr/share/myspell/ See also the DICPATH environment variable. ---- You can see which dictionary is selected if you right-click in a text area and open the Languages sub menu. At least one dictionary should be installed and have a check mark to indicate that it is selected. *open the "Add Dictionaries" link to install a dictionary if you do not have one. The spelling checker is enabled if [X] "Check Spelling" in the right-click context menu has a checkmark. You can enable or disable spell checking globally: *Settings -> General: Language and Appearance: "Check your spelling as you type" *https://support.mozilla.org/en-US/kb/how-do-i-use-firefox-spell-checker