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

Make sure you are using the correct dictionary.

I also recommend:
Grammarly for Firefox by Grammarly https://addons.mozilla.org/en-US/firefox/addon/grammarly-1/

Grammarly will help you communicate more effectively. As you type, Grammarly flags mistakes and helps you make sure your messages, documents, and social media posts are clear, mistake-free, and impactful.

Thank you but how do I point it to the default MacOS dictionary instead of the spellchecker that is normally set up to use within Firefox? It just does not have enough words in it

Did you check out

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

I did. It's just not robust enough. MacOS seems to have a considerable number of words in its default dictionary that Firefox's dictionary doesn't recognize (like "MacOS" which is underlined in red in my browser unless I have Firefox's dictionary learn it).

Thanks for your help, FredMcD.

Right-click a 'misspelled' word. One of the choices is to add that word.

I understand. The problem is there are hundreds of words I would have to add to Firefox dictionary that I already have added to macOS dictionary.

Is there anyway I can simply use the dictionary I have already saved everything to you instead of having to tell the Firefox dictionary to learn the same words again?

I called for more help.

Thank you! I very much appreciate your assistance since I don't know who to call.

Hello jwearly,

Stab in the dark, but would this extension do what you want (?) :

https://addons.mozilla.org/en-US/firefox/addon/macos-dictionary-lookup/

Thank you, McCoy, for your help. Unfortunately, that didn't work, either. After installing the extension (and verifying that it's present and active), the word "Musculoskeletal" is recognized in my Safari and Word apps but not in Firefox.

On another note, is there a way to have the Firefox spell checker ignore acronyms in all caps? It spell checks everything but I would like to have it ignore words in all caps.

Thanks!

Any update on this issue?

Any update on this issue?

Not yet.

FredMcD, Did you find out anything when you called Mozilla?

I escalated your question. That is all I can do.

Thanks!