You only need to install a dictionary for spell checking as shown in "about:addons -> Dictionaries", a language pack is used to translate strings in the user interface.

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

You can look here for dictionaries:

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

Note that for spell check you need a dictionary. A language pack provides string translations for the user interface.

• https://support.mozilla.org/en-US/kb/use-firefox-another-language

You can check in about:config whether layout.spellcheckDefault is set to 1 (multi-line) or 2 (single-line).

The screenshot shows a normal context menu and not the context menu of a text area or content editable element.

You can right-click and select "Inspect" to open the built-in Inspector with this element selected.

• https://firefox-source-docs.mozilla.org/devtools-user/page_inspector/how_to/open_the_inspector/
• https://firefox-source-docs.mozilla.org/devtools-user/page_inspector/how_to/examine_and_edit_html/

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