Note that a language pack only includes translations of strings in the user interface and doesn't include a dictionary.

Do you have a dictionary installed and selected?

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 -> Advanced: General: Browsing: "Check my spelling as I type"

You can look here for dictionaries:

• https://addons.mozilla.org/firefox/language-tools/

Installing the language pack and dictionary fixed the problem for me, but I think the language was already installed (isn't this part of the install?). Seems strange to build in the spell-check functionality without including the dictionary necessary for it to work.

Tolqua.

A lot of dictionaries have a specific license that prevents Mozilla from including the dictionary as part of the installation. In such cases you will have to install the dictionary yourself.

Thanks for the explanation, cor-el.

Tolqua.