Type about:config<enter> in the address bar. If a warning screen comes up, press the I Accept the Risk button. At the top of the screen is a search bar.

Type: layout.spellcheckDefault Its values are; 0 Spell Checker Off 1 Check Only Multi-Line Input Boxes. 2 Check Multi And Single Line Input Boxes.

Also, check the spellchecker.dictionary entry.

https://support.mozilla.org/en-US/kb/how-do-i-use-firefox-spell-checker

Start Firefox in Safe Mode {web link}

A small dialog should appear. Click Start In Safe Mode (not Refresh). Is the problem still there?

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 look here for dictionaries:

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

Note that you need a dictionary and not a language pack that provides string translations for the user interface.

layout.spellcheckDefault was set to 1, now set to 2

en-gb The dictionary was loaded and enable

Restarting in Safe Mode the spell checker doesn't work at all, no squiggley line under gibberish - I assume that's because the dictionary is an add-on.

Restarting again with add-ons enable and > jdkjjdjd < was recognised as rubbish.

" worng " was recognised and a right click offered "wrong" as the suggestion - so we're back in business.

Thanks FredMcD.

Any idea how did this got screwed up?

Glad to help. Safe Surfing. It could have been a corrupt file that was overwritten