Single line boxes are treated differently than multiple line boxes but you can fix, the problem is probably that you need to create a create persdict.dat file in your profile. Strange that some people can start right in and others (like myself) could not.

• http://dmcritchie.mvps.org/firefox/tab_capacity/001_with_underscore.htm#spellcheck
• http://dmcritchie.mvps.org/firefox/tab_capacity/001_with_underscore.htm#jumpstart

Once working find your other user dictionaries for other applications and spell check them to improve your Firefox dictionary.

Okay, spell check seems to be working here (this forum). So maybe my problem is not Firefox. Spell check is not working on the Apple Support Community Forum. I'll check there to see if others are having this problem.

Thanks.

Okay, back from Apple Support. Apparently Apple in there wisdom has found a way to turn off spell checking as you type. They have a button to spell check the entire message instead. Hmmm. Way to go Apple.

Websites can disable spell checking.
Google does the same on the Google Translate site

• https://developer.mozilla.org/en/Controlling_spell_checking_in_HTML_forms