Try Grammarly: https://addons.mozilla.org/en-US/firefox/addon/grammarly-1/

Sorry not what I wanted too complex .

Do you see a "Check Spelling" item in the right-click context menu? Is this a plain text editor like this forum uses or a rich text editor that shows formatted text? ---- 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: *Options/Preferences -> General: Browsing: "Check my spelling as I type" You can look here for dictionaries: *https://addons.mozilla.org/firefox/language-tools/