I had that already. Firefox underlines a word to tell me that it's mispelled (like here) but it doesnt provide any correct spelling for the word, like TextEdit does. In TextEdit I key in Command-Shift-: and a little window pops up showing various words spelled like the mispelled one, from which I can choose a replacement. I have the same program in my old Safari browser, but not Firefox which I use all the time now.Spell check in Firefox? (I assume that you did not actually want "SpelCheck", as that would be a bit ironic... )
Launch Firefox - Go to Preferences, the General tab. Scroll down a bit to the Language section.
Check the box "Check your spelling as you type"
I found a FireFox support page with some tips if the spell check stops working.
I tried that URL and mdea sure I had the two dictionaries installed in Firefox, restarted FF, but still no SpellChecker other than underlining mdea.Yes, one of the tips on that page is to reset the dictionary that is used. The spell check gets the replacement choices from a dictionary file (or from multiple dictionary files). So, the tips come from the idea that the spell check module can't find the database (the dictionary file) where those words are stored.
I think that FireFox spell check does not use the spell check that is built-in to the Mac system, but uses its own internal dictionary (I could be wrong about that). TextEdit, being one of the native Apple apps (as well as Safari, of course) always uses the native system spelling dictionaries, as well as the keyboard shortcuts that you know. Looks like Firefox sometimes loses track of the spelling library. The tips in the link that I found may help with that.