Define a specific spelling language

Hi The settings in "Options/Preferences -> General -> Language and Appearance" is about the language for the user interface and about the preferred language for webpages. *https://support.mozilla.org/en-US/kb/use-firefox-another-language *https://support.mozilla.org/en-US/kb/choose-display-languages-multilingual-webpages For spell check you need to install a spell check dictionary. It is possible that you confused dictionary with language pack and that you actually do not have a dictionary installed. 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 look here for dictionaries: *https://addons.mozilla.org/firefox/language-tools/ Note that for spell check you need a dictionary. You can check on the <b>about:config</b> page that <b>layout.spellcheckDefault</b> is set to 1 (multi-line) or 2 (single-line). *https://support.mozilla.org/en-US/kb/about-config-editor-firefox